Avoid trailing zeroes in printf

Question

I keep stumbling on the format specifiers for the printf   family of functions   What I want is to be able to print a double  or float  with a maximum given number of digits after the decimal point   If I use   printf   1 3f   359 01335   printf   1 3f   359 00999     I get  359 013 359 010   Instead of the desired  359 013 359 01   Can anybody help me

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Here is my first try at an answer    void xprintfloat char  format  float f      char s 50     char  p     sprintf s  format  f     for p s   p    p      if         p          while    p         while  0    --p   p     0           printf   s   s       Known bugs  Possible buffer overflow depending on format  If     is present for other reason than  f wrong result might happen

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This can t be done with the normal printf format specifiers   The closest you could get would be   printf    6g   359 013      359 013 printf    6g   359 01       359 01   but the   6  is the total numeric width so  printf    6g   3 01357      3 01357   breaks it   What you can do is to sprintf    20g   the number to a string buffer then manipulate the string to only have N characters past the decimal point   Assuming your number is in the variable num  the following function will remove all but the first N decimals  then strip off the trailing zeros  and decimal point if they were all zeros    char str 50   sprintf  str    20g  num       Make the number  morphNumericString  str  3          void morphNumericString  char  s  int n        char  p      int count       p   strchr  s                  Find decimal point  if any      if  p    NULL            count   n                  Adjust for more or less decimals          while  count  gt   0          Maximum decimals allowed               count--               if   p      0         If there s less than desired                   break               p                     Next character                      p--     0                 Truncate string          while   p     0            Remove trailing zeros               p--     0            if   p                     If all decimals were zeros  remove                   p     0                         If you re not happy with the truncation aspect  which would turn 0 12399 into 0 123 rather than rounding it to 0 124   you can actually use the rounding facilities already provided by printf  You just need to analyse the number before-hand to dynamically create the widths  then use those to turn the number into a string    include  lt stdio h gt   void nDecimals  char  s  double d  int n        int sz  double d2          Allow for negative       d2    d  gt   0    d   -d      sz    d  gt   0    0   1          Add one for each whole digit  0 xx special case        if  d2  lt  1  sz        while  d2  gt   1    d2    10 0  sz              Adjust for decimal point and fractionals       sz    1   n          Create format string then use it       sprintf  s       f   sz  n  d      int main  void        char str 50       double num       40  359 01335  -359 00999          359 01  3 01357  0 111111111  1 1223344        for  int i   0  i  lt  sizeof num  sizeof  num   i              nDecimals  str  num i   3           printf    30 20f - gt   s n   num i   str             return 0      The whole point of nDecimals   in this case is to correctly work out the field widths  then format the number using a format string based on that  The test harness main   shows this in action     40 00000000000000000000 - gt  40 000  359 01335000000000263753 - gt  359 013 -359 00999000000001615263 - gt  -359 010  359 00999999999999090505 - gt  359 010    3 01357000000000008200 - gt  3 014    0 11111111099999999852 - gt  0 111    1 12233439999999995429 - gt  1 122   Once you have the correctly rounded value  you can once again pass that to morphNumericString   to remove trailing zeros by simply changing   nDecimals  str  num i   3     into   nDecimals  str  num i   3   morphNumericString  str  3      or calling morphNumericString at the end of nDecimals but  in that case  I d probably just combine the two into one function   and you end up with     40 00000000000000000000 - gt  40  359 01335000000000263753 - gt  359 013 -359 00999000000001615263 - gt  -359 01  359 00999999999999090505 - gt  359 01    3 01357000000000008200 - gt  3 014    0 11111111099999999852 - gt  0 111    1 12233439999999995429 - gt  1 122

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This can t be done with the normal printf format specifiers   The closest you could get would be   printf    6g   359 013      359 013 printf    6g   359 01       359 01   but the   6  is the total numeric width so  printf    6g   3 01357      3 01357   breaks it   What you can do is to sprintf    20g   the number to a string buffer then manipulate the string to only have N characters past the decimal point   Assuming your number is in the variable num  the following function will remove all but the first N decimals  then strip off the trailing zeros  and decimal point if they were all zeros    char str 50   sprintf  str    20g  num       Make the number  morphNumericString  str  3          void morphNumericString  char  s  int n        char  p      int count       p   strchr  s                  Find decimal point  if any      if  p    NULL            count   n                  Adjust for more or less decimals          while  count  gt   0          Maximum decimals allowed               count--               if   p      0         If there s less than desired                   break               p                     Next character                      p--     0                 Truncate string          while   p     0            Remove trailing zeros               p--     0            if   p                     If all decimals were zeros  remove                   p     0                         If you re not happy with the truncation aspect  which would turn 0 12399 into 0 123 rather than rounding it to 0 124   you can actually use the rounding facilities already provided by printf  You just need to analyse the number before-hand to dynamically create the widths  then use those to turn the number into a string    include  lt stdio h gt   void nDecimals  char  s  double d  int n        int sz  double d2          Allow for negative       d2    d  gt   0    d   -d      sz    d  gt   0    0   1          Add one for each whole digit  0 xx special case        if  d2  lt  1  sz        while  d2  gt   1    d2    10 0  sz              Adjust for decimal point and fractionals       sz    1   n          Create format string then use it       sprintf  s       f   sz  n  d      int main  void        char str 50       double num       40  359 01335  -359 00999          359 01  3 01357  0 111111111  1 1223344        for  int i   0  i  lt  sizeof num  sizeof  num   i              nDecimals  str  num i   3           printf    30 20f - gt   s n   num i   str             return 0      The whole point of nDecimals   in this case is to correctly work out the field widths  then format the number using a format string based on that  The test harness main   shows this in action     40 00000000000000000000 - gt  40 000  359 01335000000000263753 - gt  359 013 -359 00999000000001615263 - gt  -359 010  359 00999999999999090505 - gt  359 010    3 01357000000000008200 - gt  3 014    0 11111111099999999852 - gt  0 111    1 12233439999999995429 - gt  1 122   Once you have the correctly rounded value  you can once again pass that to morphNumericString   to remove trailing zeros by simply changing   nDecimals  str  num i   3     into   nDecimals  str  num i   3   morphNumericString  str  3      or calling morphNumericString at the end of nDecimals but  in that case  I d probably just combine the two into one function   and you end up with     40 00000000000000000000 - gt  40  359 01335000000000263753 - gt  359 013 -359 00999000000001615263 - gt  -359 01  359 00999999999999090505 - gt  359 01    3 01357000000000008200 - gt  3 014    0 11111111099999999852 - gt  0 111    1 12233439999999995429 - gt  1 122

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I would say you should use  printf    8g  value     If you use    6g  you will not get desired output for some numbers like 32 230210 it should print 32 23021 but it prints 32 2302

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I found problems in some of the solutions posted   I put this together based on answers above   It seems to work for me   int doubleEquals double i  double j        return  fabs i - j   lt  0 000001      void printTruncatedDouble double dd  int max len        char str 50       int match   0      for   int ii   0  ii  lt  max len  ii               if  doubleEquals dd   pow 10 ii   floor dd   pow 10 ii                   sprintf  str   f   round dd pow 10 ii   pow 10 ii                match   1              break                      if   match    1             sprintf  str   f   round dd pow 10 max len   pow 10 max len              char  pp      int count      pp   strchr  str           if  pp    NULL            count   max len          while  count  gt   0                 count--               if   pp      0                    break               pp                       pp--     0           while   pp     0                pp--     0           if   pp                        pp     0                       printf    s n   str      int main int argc  char   argv        printTruncatedDouble  -1 999  2       prints -2     printTruncatedDouble  -1 006  2       prints -1 01     printTruncatedDouble  -1 005  2       prints -1     printf   n        printTruncatedDouble  1 005  2       prints 1  should be 1 01       printTruncatedDouble  1 006  2       prints 1 01     printTruncatedDouble  1 999  2       prints 2     printf   n        printTruncatedDouble  -1 999  3       prints -1 999     printTruncatedDouble  -1 001  3       prints -1 001     printTruncatedDouble  -1 0005  3       prints -1 001  shound be -1       printTruncatedDouble  -1 0004  3       prints -1     printf   n        printTruncatedDouble  1 0004  3       prints 1     printTruncatedDouble  1 0005  3       prints 1 001     printTruncatedDouble  1 001  3       prints 1 001     printTruncatedDouble  1 999  3       prints 1 999     printf   n        exit 0

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This can t be done with the normal printf format specifiers   The closest you could get would be   printf    6g   359 013      359 013 printf    6g   359 01       359 01   but the   6  is the total numeric width so  printf    6g   3 01357      3 01357   breaks it   What you can do is to sprintf    20g   the number to a string buffer then manipulate the string to only have N characters past the decimal point   Assuming your number is in the variable num  the following function will remove all but the first N decimals  then strip off the trailing zeros  and decimal point if they were all zeros    char str 50   sprintf  str    20g  num       Make the number  morphNumericString  str  3          void morphNumericString  char  s  int n        char  p      int count       p   strchr  s                  Find decimal point  if any      if  p    NULL            count   n                  Adjust for more or less decimals          while  count  gt   0          Maximum decimals allowed               count--               if   p      0         If there s less than desired                   break               p                     Next character                      p--     0                 Truncate string          while   p     0            Remove trailing zeros               p--     0            if   p                     If all decimals were zeros  remove                   p     0                         If you re not happy with the truncation aspect  which would turn 0 12399 into 0 123 rather than rounding it to 0 124   you can actually use the rounding facilities already provided by printf  You just need to analyse the number before-hand to dynamically create the widths  then use those to turn the number into a string    include  lt stdio h gt   void nDecimals  char  s  double d  int n        int sz  double d2          Allow for negative       d2    d  gt   0    d   -d      sz    d  gt   0    0   1          Add one for each whole digit  0 xx special case        if  d2  lt  1  sz        while  d2  gt   1    d2    10 0  sz              Adjust for decimal point and fractionals       sz    1   n          Create format string then use it       sprintf  s       f   sz  n  d      int main  void        char str 50       double num       40  359 01335  -359 00999          359 01  3 01357  0 111111111  1 1223344        for  int i   0  i  lt  sizeof num  sizeof  num   i              nDecimals  str  num i   3           printf    30 20f - gt   s n   num i   str             return 0      The whole point of nDecimals   in this case is to correctly work out the field widths  then format the number using a format string based on that  The test harness main   shows this in action     40 00000000000000000000 - gt  40 000  359 01335000000000263753 - gt  359 013 -359 00999000000001615263 - gt  -359 010  359 00999999999999090505 - gt  359 010    3 01357000000000008200 - gt  3 014    0 11111111099999999852 - gt  0 111    1 12233439999999995429 - gt  1 122   Once you have the correctly rounded value  you can once again pass that to morphNumericString   to remove trailing zeros by simply changing   nDecimals  str  num i   3     into   nDecimals  str  num i   3   morphNumericString  str  3      or calling morphNumericString at the end of nDecimals but  in that case  I d probably just combine the two into one function   and you end up with     40 00000000000000000000 - gt  40  359 01335000000000263753 - gt  359 013 -359 00999000000001615263 - gt  -359 01  359 00999999999999090505 - gt  359 01    3 01357000000000008200 - gt  3 014    0 11111111099999999852 - gt  0 111    1 12233439999999995429 - gt  1 122

User · Answer

Why not just do this   double f   359 01335  printf   g   round f   1000 0    1000 0

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A simple solution but it gets the job done  assigns a known length and precision and avoids the chance of going exponential format  which is a risk when you use  g       Since we are only interested in 3 decimal places  this function    can avoid any potential miniscule floating point differences    which can return false when using      int DoubleEquals double i  double j        return  fabs i - j   lt  0 000001      void PrintMaxThreeDecimal double d        if  DoubleEquals d  floor d            printf    0f   d       else if  DoubleEquals d   10  floor d   10            printf    1f   d       else if  DoubleEquals d   100  floor d  100            printf    2f   d       else         printf    3f   d       Add or remove  elses  if you want a max of 2 decimals  4 decimals  etc   For example if you wanted 2 decimals   void PrintMaxTwoDecimal double d        if  DoubleEquals d  floor d            printf    0f   d       else if  DoubleEquals d   10  floor d   10            printf    1f   d       else         printf    2f   d       If you want to specify the minimum width to keep fields aligned  increment as necessary  for example   void PrintAlignedMaxThreeDecimal double d        if  DoubleEquals d  floor d            printf   7 0f   d       else if  DoubleEquals d   10  floor d   10            printf   9 1f   d       else if  DoubleEquals d   100  floor d  100            printf   10 2f   d       else         printf   11 3f   d       You could also convert that to a function where you pass the desired width of the field   void PrintAlignedWidthMaxThreeDecimal int w  double d        if  DoubleEquals d  floor d            printf     0f   w-4  d       else if  DoubleEquals d   10  floor d   10            printf     1f   w-2  d       else if  DoubleEquals d   100  floor d  100            printf     2f   w-1  d       else         printf     3f   w  d

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Here is my first try at an answer    void xprintfloat char  format  float f      char s 50     char  p     sprintf s  format  f     for p s   p    p      if         p          while    p         while  0    --p   p     0           printf   s   s       Known bugs  Possible buffer overflow depending on format  If     is present for other reason than  f wrong result might happen

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A simple solution but it gets the job done  assigns a known length and precision and avoids the chance of going exponential format  which is a risk when you use  g       Since we are only interested in 3 decimal places  this function    can avoid any potential miniscule floating point differences    which can return false when using      int DoubleEquals double i  double j        return  fabs i - j   lt  0 000001      void PrintMaxThreeDecimal double d        if  DoubleEquals d  floor d            printf    0f   d       else if  DoubleEquals d   10  floor d   10            printf    1f   d       else if  DoubleEquals d   100  floor d  100            printf    2f   d       else         printf    3f   d       Add or remove  elses  if you want a max of 2 decimals  4 decimals  etc   For example if you wanted 2 decimals   void PrintMaxTwoDecimal double d        if  DoubleEquals d  floor d            printf    0f   d       else if  DoubleEquals d   10  floor d   10            printf    1f   d       else         printf    2f   d       If you want to specify the minimum width to keep fields aligned  increment as necessary  for example   void PrintAlignedMaxThreeDecimal double d        if  DoubleEquals d  floor d            printf   7 0f   d       else if  DoubleEquals d   10  floor d   10            printf   9 1f   d       else if  DoubleEquals d   100  floor d  100            printf   10 2f   d       else         printf   11 3f   d       You could also convert that to a function where you pass the desired width of the field   void PrintAlignedWidthMaxThreeDecimal int w  double d        if  DoubleEquals d  floor d            printf     0f   w-4  d       else if  DoubleEquals d   10  floor d   10            printf     1f   w-2  d       else if  DoubleEquals d   100  floor d  100            printf     2f   w-1  d       else         printf     3f   w  d

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Here is my first try at an answer    void xprintfloat char  format  float f      char s 50     char  p     sprintf s  format  f     for p s   p    p      if         p          while    p         while  0    --p   p     0           printf   s   s       Known bugs  Possible buffer overflow depending on format  If     is present for other reason than  f wrong result might happen

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This can t be done with the normal printf format specifiers   The closest you could get would be   printf    6g   359 013      359 013 printf    6g   359 01       359 01   but the   6  is the total numeric width so  printf    6g   3 01357      3 01357   breaks it   What you can do is to sprintf    20g   the number to a string buffer then manipulate the string to only have N characters past the decimal point   Assuming your number is in the variable num  the following function will remove all but the first N decimals  then strip off the trailing zeros  and decimal point if they were all zeros    char str 50   sprintf  str    20g  num       Make the number  morphNumericString  str  3          void morphNumericString  char  s  int n        char  p      int count       p   strchr  s                  Find decimal point  if any      if  p    NULL            count   n                  Adjust for more or less decimals          while  count  gt   0          Maximum decimals allowed               count--               if   p      0         If there s less than desired                   break               p                     Next character                      p--     0                 Truncate string          while   p     0            Remove trailing zeros               p--     0            if   p                     If all decimals were zeros  remove                   p     0                         If you re not happy with the truncation aspect  which would turn 0 12399 into 0 123 rather than rounding it to 0 124   you can actually use the rounding facilities already provided by printf  You just need to analyse the number before-hand to dynamically create the widths  then use those to turn the number into a string    include  lt stdio h gt   void nDecimals  char  s  double d  int n        int sz  double d2          Allow for negative       d2    d  gt   0    d   -d      sz    d  gt   0    0   1          Add one for each whole digit  0 xx special case        if  d2  lt  1  sz        while  d2  gt   1    d2    10 0  sz              Adjust for decimal point and fractionals       sz    1   n          Create format string then use it       sprintf  s       f   sz  n  d      int main  void        char str 50       double num       40  359 01335  -359 00999          359 01  3 01357  0 111111111  1 1223344        for  int i   0  i  lt  sizeof num  sizeof  num   i              nDecimals  str  num i   3           printf    30 20f - gt   s n   num i   str             return 0      The whole point of nDecimals   in this case is to correctly work out the field widths  then format the number using a format string based on that  The test harness main   shows this in action     40 00000000000000000000 - gt  40 000  359 01335000000000263753 - gt  359 013 -359 00999000000001615263 - gt  -359 010  359 00999999999999090505 - gt  359 010    3 01357000000000008200 - gt  3 014    0 11111111099999999852 - gt  0 111    1 12233439999999995429 - gt  1 122   Once you have the correctly rounded value  you can once again pass that to morphNumericString   to remove trailing zeros by simply changing   nDecimals  str  num i   3     into   nDecimals  str  num i   3   morphNumericString  str  3      or calling morphNumericString at the end of nDecimals but  in that case  I d probably just combine the two into one function   and you end up with     40 00000000000000000000 - gt  40  359 01335000000000263753 - gt  359 013 -359 00999000000001615263 - gt  -359 01  359 00999999999999090505 - gt  359 01    3 01357000000000008200 - gt  3 014    0 11111111099999999852 - gt  0 111    1 12233439999999995429 - gt  1 122

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I would say you should use  printf    8g  value     If you use    6g  you will not get desired output for some numbers like 32 230210 it should print 32 23021 but it prints 32 2302

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I like the answer of R  slightly tweaked   float f   1234 56789  printf   d   0f   f  1000  f- int f       1000  determines the precision   Power to the 0 5 rounding   EDIT  Ok  this answer was edited a few times and I lost track what I was thinking a few years back  and originally it did not fill all the criteria   So here is a new version  that fills all criteria and handles negative numbers correctly    double f   1234 05678900  char s 100    int decimals   10   sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals    printf  10 decimals   d s n    int f  s 1     And the test cases    import  lt stdio h gt   import  lt stdlib h gt   import  lt math h gt   int main void        double f   1234 05678900      char s 100       int decimals       decimals   10      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf  10 decimals   d s n    int f  s 1        decimals   3      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf   3 decimals   d s n    int f  s 1        f   -f      decimals   10      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf   negative 10   d s n    int f  s 1        decimals   3      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf   negative  3   d s n    int f  s 1        decimals   2      f   1 012      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf   additional    d s n    int f  s 1        return 0      And the output of the tests    10 decimals  1234 056789   3 decimals  1234 057  negative 10  -1234 056789  negative  3  -1234 057  additional   1 01   Now  all criteria are met    maximum number of decimals behind the zero is fixed trailing zeros are removed it does it mathematically right  right   works  now  also when first decimal is zero    Unfortunately this answer is a two-liner as sprintf does not return the string

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Some of the highly voted solutions suggest the  g conversion specifier of printf  This is wrong because there are cases where  g will produce scientific notation  Other solutions use math to print the desired number of decimal digits   I think the easiest solution is to use sprintf with the  f conversion specifier and to manually remove trailing zeros and possibly a decimal point from the result  Here s a C99 solution    include  lt stdio h gt   include  lt stdlib h gt   char  format double double d        int size   snprintf NULL  0     3f   d       char  str   malloc size   1       snprintf str  size   1     3f   d        for  int i   size - 1  end   size  i  gt   0  i--            if  str i      0                 if  end    i   1                    end   i                                  else if  str i                        if  end    i   1                    end   i                            str end      0               break                       return str      Note that the characters used for digits and the decimal separator depend on the current locale  The code above assumes a C or US English locale

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I search the string  starting rightmost  for the first character in the range 1 to 9  ASCII value 49-57  then null  set to 0  each char right of it - see below   void stripTrailingZeros void           This finds the index of the rightmost ASCII char 1-9  in array       All elements to the left of this are nulled   0      int i   20      unsigned char char1   0    initialised to ensure entry to condition below      while   char1  gt  57      char1  lt  49             i--          char1   sprintfBuffer i                null chars left of i     for  int j   i  j  lt  20  j              sprintfBuffer i    0

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To get rid of the trailing zeros  you should use the   g  format   float num   1 33  printf   g   num     output  1 33   After the question was clarified a bit  that suppressing zeros is not the only thing that was asked  but limiting the output to three decimal places was required as well  I think that can t be done with sprintf format strings alone  As Pax Diablo pointed out  string manipulation would be required

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Here is my first try at an answer    void xprintfloat char  format  float f      char s 50     char  p     sprintf s  format  f     for p s   p    p      if         p          while    p         while  0    --p   p     0           printf   s   s       Known bugs  Possible buffer overflow depending on format  If     is present for other reason than  f wrong result might happen

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Your code rounds to three decimal places due to the   3  before the f  printf   1 3f   359 01335   printf   1 3f   359 00999     Thus if you the second line rounded to two decimal places  you should change it to this   printf   1 3f   359 01335   printf   1 2f   359 00999     That code will output your desired results   359 013 359 01    Note this is assuming you already have it printing on separate lines  if not then the following will prevent it from printing on the same line   printf   1 3f n   359 01335   printf   1 2f n   359 00999     The Following program source code was my test for this answer   include  lt cstdio gt   int main          printf   1 3f n   359 01335       printf   1 2f n   359 00999        while  true         return 0

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Slight variation on above    Eliminates period for case  10000 0   Breaks after first period is processed    Code here   void EliminateTrailingFloatZeros char  iValue      char  p   0    for p iValue   p    p        if         p          while    p         while  0    --p   p     0         if  p          p     0         break                It still has potential for overflow  so be careful  P

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Some of the highly voted solutions suggest the  g conversion specifier of printf  This is wrong because there are cases where  g will produce scientific notation  Other solutions use math to print the desired number of decimal digits   I think the easiest solution is to use sprintf with the  f conversion specifier and to manually remove trailing zeros and possibly a decimal point from the result  Here s a C99 solution    include  lt stdio h gt   include  lt stdlib h gt   char  format double double d        int size   snprintf NULL  0     3f   d       char  str   malloc size   1       snprintf str  size   1     3f   d        for  int i   size - 1  end   size  i  gt   0  i--            if  str i      0                 if  end    i   1                    end   i                                  else if  str i                        if  end    i   1                    end   i                            str end      0               break                       return str      Note that the characters used for digits and the decimal separator depend on the current locale  The code above assumes a C or US English locale

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To get rid of the trailing zeros  you should use the   g  format   float num   1 33  printf   g   num     output  1 33   After the question was clarified a bit  that suppressing zeros is not the only thing that was asked  but limiting the output to three decimal places was required as well  I think that can t be done with sprintf format strings alone  As Pax Diablo pointed out  string manipulation would be required

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I search the string  starting rightmost  for the first character in the range 1 to 9  ASCII value 49-57  then null  set to 0  each char right of it - see below   void stripTrailingZeros void           This finds the index of the rightmost ASCII char 1-9  in array       All elements to the left of this are nulled   0      int i   20      unsigned char char1   0    initialised to ensure entry to condition below      while   char1  gt  57      char1  lt  49             i--          char1   sprintfBuffer i                null chars left of i     for  int j   i  j  lt  20  j              sprintfBuffer i    0

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Why not just do this   double f   359 01335  printf   g   round f   1000 0    1000 0

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I like the answer of R  slightly tweaked   float f   1234 56789  printf   d   0f   f  1000  f- int f       1000  determines the precision   Power to the 0 5 rounding   EDIT  Ok  this answer was edited a few times and I lost track what I was thinking a few years back  and originally it did not fill all the criteria   So here is a new version  that fills all criteria and handles negative numbers correctly    double f   1234 05678900  char s 100    int decimals   10   sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals    printf  10 decimals   d s n    int f  s 1     And the test cases    import  lt stdio h gt   import  lt stdlib h gt   import  lt math h gt   int main void        double f   1234 05678900      char s 100       int decimals       decimals   10      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf  10 decimals   d s n    int f  s 1        decimals   3      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf   3 decimals   d s n    int f  s 1        f   -f      decimals   10      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf   negative 10   d s n    int f  s 1        decimals   3      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf   negative  3   d s n    int f  s 1        decimals   2      f   1 012      sprintf s     g   decimals    int  pow 10  decimals   fabs f  - abs  int f    0 5   pow 10 decimals        printf   additional    d s n    int f  s 1        return 0      And the output of the tests    10 decimals  1234 056789   3 decimals  1234 057  negative 10  -1234 056789  negative  3  -1234 057  additional   1 01   Now  all criteria are met    maximum number of decimals behind the zero is fixed trailing zeros are removed it does it mathematically right  right   works  now  also when first decimal is zero    Unfortunately this answer is a two-liner as sprintf does not return the string

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To get rid of the trailing zeros  you should use the   g  format   float num   1 33  printf   g   num     output  1 33   After the question was clarified a bit  that suppressing zeros is not the only thing that was asked  but limiting the output to three decimal places was required as well  I think that can t be done with sprintf format strings alone  As Pax Diablo pointed out  string manipulation would be required

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Hit the same issue  double precision is 15 decimal  and float precision is 6 decimal  so I wrote to 2 functions for them separately  include  lt stdio h gt   include  lt math h gt   include  lt string gt   include  lt string h gt   std  string doublecompactstring double d        char buf 128     0       if  isnan d           return  quot NAN quot       sprintf buf   quot   15f quot   d          try to remove the trailing zeros     size t ccLen   strlen buf       for int i  int  ccLen -1  i gt  0 i--                if  buf i      0               buf i      0           else             break             return buf     std  string floatcompactstring float d        char buf 128     0       if  isnan d           return  quot NAN quot       sprintf buf   quot   6f quot   d          try to remove the trailing zeros     size t ccLen   strlen buf       for int i  int  ccLen -1  i gt  0 i--                if  buf i      0               buf i      0           else             break             return buf     int main int argc  const char  argv          double a   0 000000000000001      float  b   0 000001f       printf  quot a   s n quot   doublecompactstring a  c str         printf  quot b   s n quot   floatcompactstring b  c str         return 0     output is a  0 000000000000001 b  0 000001

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Slight variation on above    Eliminates period for case  10000 0   Breaks after first period is processed    Code here   void EliminateTrailingFloatZeros char  iValue      char  p   0    for p iValue   p    p        if         p          while    p         while  0    --p   p     0         if  p          p     0         break                It still has potential for overflow  so be careful  P

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I found problems in some of the solutions posted   I put this together based on answers above   It seems to work for me   int doubleEquals double i  double j        return  fabs i - j   lt  0 000001      void printTruncatedDouble double dd  int max len        char str 50       int match   0      for   int ii   0  ii  lt  max len  ii               if  doubleEquals dd   pow 10 ii   floor dd   pow 10 ii                   sprintf  str   f   round dd pow 10 ii   pow 10 ii                match   1              break                      if   match    1             sprintf  str   f   round dd pow 10 max len   pow 10 max len              char  pp      int count      pp   strchr  str           if  pp    NULL            count   max len          while  count  gt   0                 count--               if   pp      0                    break               pp                       pp--     0           while   pp     0                pp--     0           if   pp                        pp     0                       printf    s n   str      int main int argc  char   argv        printTruncatedDouble  -1 999  2       prints -2     printTruncatedDouble  -1 006  2       prints -1 01     printTruncatedDouble  -1 005  2       prints -1     printf   n        printTruncatedDouble  1 005  2       prints 1  should be 1 01       printTruncatedDouble  1 006  2       prints 1 01     printTruncatedDouble  1 999  2       prints 2     printf   n        printTruncatedDouble  -1 999  3       prints -1 999     printTruncatedDouble  -1 001  3       prints -1 001     printTruncatedDouble  -1 0005  3       prints -1 001  shound be -1       printTruncatedDouble  -1 0004  3       prints -1     printf   n        printTruncatedDouble  1 0004  3       prints 1     printTruncatedDouble  1 0005  3       prints 1 001     printTruncatedDouble  1 001  3       prints 1 001     printTruncatedDouble  1 999  3       prints 1 999     printf   n        exit 0

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What about something like this  might have rounding errors and negative-value issues that need debugging  left as an exercise for the reader    printf    0d  4g n    int f 10  f-  int f- int f 10      It s slightly programmatic but at least it doesn t make you do any string manipulation

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Your code rounds to three decimal places due to the   3  before the f  printf   1 3f   359 01335   printf   1 3f   359 00999     Thus if you the second line rounded to two decimal places  you should change it to this   printf   1 3f   359 01335   printf   1 2f   359 00999     That code will output your desired results   359 013 359 01    Note this is assuming you already have it printing on separate lines  if not then the following will prevent it from printing on the same line   printf   1 3f n   359 01335   printf   1 2f n   359 00999     The Following program source code was my test for this answer   include  lt cstdio gt   int main          printf   1 3f n   359 01335       printf   1 2f n   359 00999        while  true         return 0

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To get rid of the trailing zeros  you should use the   g  format   float num   1 33  printf   g   num     output  1 33   After the question was clarified a bit  that suppressing zeros is not the only thing that was asked  but limiting the output to three decimal places was required as well  I think that can t be done with sprintf format strings alone  As Pax Diablo pointed out  string manipulation would be required

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What about something like this  might have rounding errors and negative-value issues that need debugging  left as an exercise for the reader    printf    0d  4g n    int f 10  f-  int f- int f 10      It s slightly programmatic but at least it doesn t make you do any string manipulation

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Hit the same issue  double precision is 15 decimal  and float precision is 6 decimal  so I wrote to 2 functions for them separately  include  lt stdio h gt   include  lt math h gt   include  lt string gt   include  lt string h gt   std  string doublecompactstring double d        char buf 128     0       if  isnan d           return  quot NAN quot       sprintf buf   quot   15f quot   d          try to remove the trailing zeros     size t ccLen   strlen buf       for int i  int  ccLen -1  i gt  0 i--                if  buf i      0               buf i      0           else             break             return buf     std  string floatcompactstring float d        char buf 128     0       if  isnan d           return  quot NAN quot       sprintf buf   quot   6f quot   d          try to remove the trailing zeros     size t ccLen   strlen buf       for int i  int  ccLen -1  i gt  0 i--                if  buf i      0               buf i      0           else             break             return buf     int main int argc  const char  argv          double a   0 000000000000001      float  b   0 000001f       printf  quot a   s n quot   doublecompactstring a  c str         printf  quot b   s n quot   floatcompactstring b  c str         return 0     output is a  0 000000000000001 b  0 000001

[c] Avoid trailing zeroes in printf()

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