How do you do exponentiation in C

Question

I tried  x   y    e   but that didn t work

User · Accepted Answer

use the pow function  it takes floats doubles though    man pow       include  lt math h gt      double pow double x  double y      float powf float x  float y      long double powl long double x  long double y     EDIT  For the special case of positive integer powers of 2  you can use bit shifting   1  lt  lt  x  will equal 2 to the power x  There are some potential gotchas with this  but generally  it would be correct

User · Answer

pow only works on floating-point numbers  doubles  actually    If you want to take powers of integers  and the base isn t known to be an exponent of 2  you ll have to roll your own   Usually the dumb way is good enough   int power int base  unsigned int exp        int i  result   1      for  i   0  i  lt  exp  i            result    base      return result       Here s a recursive solution which takes O log n  space and time instead of the easy O 1  space O n  time   int power int base  int exp        if  exp    0          return 1      else if  exp   2          return base   power base  exp - 1       else           int temp   power base  exp   2           return temp   temp

User · Answer

pow only works on floating-point numbers  doubles  actually    If you want to take powers of integers  and the base isn t known to be an exponent of 2  you ll have to roll your own   Usually the dumb way is good enough   int power int base  unsigned int exp        int i  result   1      for  i   0  i  lt  exp  i            result    base      return result       Here s a recursive solution which takes O log n  space and time instead of the easy O 1  space O n  time   int power int base  int exp        if  exp    0          return 1      else if  exp   2          return base   power base  exp - 1       else           int temp   power base  exp   2           return temp   temp

User · Answer

Similar to an earlier answer  this will handle positive and negative integer powers of a double nicely   double intpow double a  int b      double r   1 0    if  b  lt  0          a   1 0   a      b   -b        while  b          if  b  amp  1        r    a      a    a      b  gt  gt   1        return r

User · Answer

The non-recursive version of the function is not too hard - here it is for integers   long powi long x  unsigned n        long p   x      long r   1       while  n  gt  0                if  n   2    1              r    p          p    p          n    2             return r        Hacked out of code for raising a double value to an integer power - had to remove the code to deal with reciprocals  for example

User · Answer

int power int x int y    int r 1   do    r  r    if y 2     r  x    while y gt  gt  1    return r        iterative   int power int x int y    return y  y 2 x 1  power x x y gt  gt 1  1        if it has to be recursive   imo  the algorithm should definitely be O logn

User · Answer

The non-recursive version of the function is not too hard - here it is for integers   long powi long x  unsigned n        long p   x      long r   1       while  n  gt  0                if  n   2    1              r    p          p    p          n    2             return r        Hacked out of code for raising a double value to an integer power - had to remove the code to deal with reciprocals  for example

User · Answer

or you could just write the power function  with recursion as a added bonus  int power int x  int y         if y    0          return 1       return  x   power x y-1             yes yes i know this is less effecient space and time complexity but recursion is just more fun

User · Answer

or you could just write the power function  with recursion as a added bonus  int power int x  int y         if y    0          return 1       return  x   power x y-1             yes yes i know this is less effecient space and time complexity but recursion is just more fun

User · Answer

To add to what Evan said  C does not have a built-in operator for exponentiation  because it is not a primitive operation for most CPUs   Thus  it s implemented as a library function   Also  for computing the function e x  you can use the exp double   expf float   and expl long double  functions   Note that you do not want to use the   operator  which is the bitwise exclusive OR operator

User · Answer

The non-recursive version of the function is not too hard - here it is for integers   long powi long x  unsigned n        long p   x      long r   1       while  n  gt  0                if  n   2    1              r    p          p    p          n    2             return r        Hacked out of code for raising a double value to an integer power - had to remove the code to deal with reciprocals  for example

User · Answer

To add to what Evan said  C does not have a built-in operator for exponentiation  because it is not a primitive operation for most CPUs   Thus  it s implemented as a library function   Also  for computing the function e x  you can use the exp double   expf float   and expl long double  functions   Note that you do not want to use the   operator  which is the bitwise exclusive OR operator

User · Answer

To add to what Evan said  C does not have a built-in operator for exponentiation  because it is not a primitive operation for most CPUs   Thus  it s implemented as a library function   Also  for computing the function e x  you can use the exp double   expf float   and expl long double  functions   Note that you do not want to use the   operator  which is the bitwise exclusive OR operator

User · Answer

pow only works on floating-point numbers  doubles  actually    If you want to take powers of integers  and the base isn t known to be an exponent of 2  you ll have to roll your own   Usually the dumb way is good enough   int power int base  unsigned int exp        int i  result   1      for  i   0  i  lt  exp  i            result    base      return result       Here s a recursive solution which takes O log n  space and time instead of the easy O 1  space O n  time   int power int base  int exp        if  exp    0          return 1      else if  exp   2          return base   power base  exp - 1       else           int temp   power base  exp   2           return temp   temp

User · Answer

or you could just write the power function  with recursion as a added bonus  int power int x  int y         if y    0          return 1       return  x   power x y-1             yes yes i know this is less effecient space and time complexity but recursion is just more fun

User · Answer

or you could just write the power function  with recursion as a added bonus  int power int x  int y         if y    0          return 1       return  x   power x y-1             yes yes i know this is less effecient space and time complexity but recursion is just more fun

User · Answer

The non-recursive version of the function is not too hard - here it is for integers   long powi long x  unsigned n        long p   x      long r   1       while  n  gt  0                if  n   2    1              r    p          p    p          n    2             return r        Hacked out of code for raising a double value to an integer power - had to remove the code to deal with reciprocals  for example

User · Answer

pow only works on floating-point numbers  doubles  actually    If you want to take powers of integers  and the base isn t known to be an exponent of 2  you ll have to roll your own   Usually the dumb way is good enough   int power int base  unsigned int exp        int i  result   1      for  i   0  i  lt  exp  i            result    base      return result       Here s a recursive solution which takes O log n  space and time instead of the easy O 1  space O n  time   int power int base  int exp        if  exp    0          return 1      else if  exp   2          return base   power base  exp - 1       else           int temp   power base  exp   2           return temp   temp

User · Answer

Similar to an earlier answer  this will handle positive and negative integer powers of a double nicely   double intpow double a  int b      double r   1 0    if  b  lt  0          a   1 0   a      b   -b        while  b          if  b  amp  1        r    a      a    a      b  gt  gt   1        return r

User · Answer

int power int x int y    int r 1   do    r  r    if y 2     r  x    while y gt  gt  1    return r        iterative   int power int x int y    return y  y 2 x 1  power x x y gt  gt 1  1        if it has to be recursive   imo  the algorithm should definitely be O logn

User · Answer

To add to what Evan said  C does not have a built-in operator for exponentiation  because it is not a primitive operation for most CPUs   Thus  it s implemented as a library function   Also  for computing the function e x  you can use the exp double   expf float   and expl long double  functions   Note that you do not want to use the   operator  which is the bitwise exclusive OR operator

[c] How do you do exponentiation in C?

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