C pass int array pointer as parameter into a function

Question

I want to pass the B int array pointer into func function and be able to change it from there and then view the changes in main function   include  lt stdio h gt   int func int  B 10        int main void        int  B 10        func  amp B        return 0      the above code gives me some errors   In function  main    warning  passing argument 1 of  func  from incompatible pointer type  enabled by default   note  expected  int     but argument is of type  int       10      EDIT  new code    include  lt stdio h gt   int func int  B        B 0    5     int main void        int B 10     NULL       printf  b 0     d n n   B 0        func B       printf  b 0     d n n   B 0         return 0      now i get these errors     In function  func     4 error  invalid type argument of unary      have  int      In function  main     9 warning  initialization makes integer from pointer without a cast  enabled by default    9 warning   near initialization for  B 0     enabled by default         Build finished  1 errors  2 warnings

User · Answer

Make use of   B  instead of  B 0   Here     B i  implies B i  and   B  implies B 0   that is   B 0    B  B 0     include  lt stdio h gt   int func int  B        B   5              if you want to modify ith index element in the array just do   B i   lt value gt     int main void        int B 10            printf  b 0     d n n   B 0        func B       printf  b 0     d n n   B 0        return 0

User · Answer

In new code assignment should be   B 0    5   In func B   you are just passing address of the pointer which is pointing to array B  You can do change in func   as B i  or   B   i   Where i is the index of the array   In the first code the declaration says    int  B 10    says that B is an array of 10 elements  each element of which is a pointer to a int  That is  B i  is a int pointer and  B i  is the integer it points to the first integer of the i-th saved text line

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The argument of func is accepting double-pointer variable  Hope this helps      include  lt stdio h gt   int func int   B       int main void        int  B 10        func B        return 0

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Using the really excellent example from Greggo  I got this to work as a bubble sort with passing an array as a pointer and doing a simple -1 manipulation    include lt stdio h gt   void sub one int   arr  7          int i        for i 0 i lt 7 i                    arr  i  -  1      subtract 1 from each point         printf   i n     arr  i                  int main         int a      180  185  190  175  200  180  181       int pos  j  i      int n 7      int temp      for  pos  0  pos  lt  7  pos              printf   nPosition  i Value  i   pos  a pos              for i 1 i lt  n-1 i             temp a i           j i-1          while  temp lt a j   amp  amp  j gt  0      while selected   less than a j  and not j isn t 0                       a j 1  a j        moves element forward             j j-1                     a j 1  temp       insert element in proper place            printf   nSorted list is as follows  n        for i 0 i lt n i                  printf   d n  a i              printf   nmedian    d n   a 3        sub one  amp a        return 0      I need to read up on how to encapsulate pointers because that threw me off

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If you actually want to pass an array pointer  it s   include  lt stdio h gt   void func int   B  10         ptr to array of 10 ints            B  0    5       note   B 0  means   B 0              B 0  0    5      same  but could be misleading here  see below     int main void            int B 10     0        not NULL  which is for pointers          printf  b 0     d n n   B 0            func  amp B                  amp B is ptr to arry of 10 ints          printf  b 0     d n n   B 0             return 0      But as mentioned in other answers  it s not that common to do this  Usually a pointer-to-array is passed only when you want to pass a 2d array  where it suddenly looks a lot clearer  as below  A 2D array is actually passed as a pointer to its first row   void func  int B 5  10        this func is actually the same as the one above              B 0  0    5     int main void       int Ar2D 5  10       func Ar2D        same as func   amp Ar2D 0        The parameter of func may be declared as int B 5  10   int B   10    int   B  10   all are equivalent as parameter types    Addendum  you can return a pointer-to-array from a function  but the syntax to declare the function is very awkward  the  10  part of the type has to go after the parameter list   int MyArr 5  10   int MyRow 10    int   select myarr row  int i    10       yes  really    return  i gt  0  amp  amp  i lt 5    amp MyArr i     amp MyRow      This is usually done as below  to avoid eyestrain   typedef int   pa10int  10    pa10int select myarr row  int i        return  i gt  0  amp  amp  i lt 5    amp MyArr i     amp MyRow

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In the function declaration you have to type as  VOID FUN INT  a       HERE YOU CAN TAKE ANY FUNCTION RETURN TYPE HERE I CAN TAKE VOID AS THE FUNCTION RETURN  TYPE FOR THE FUNCTION FUN     IN THE FUNCTION HEADER WE CAN WRITE AS FOLLOWS void fun int  a      in the function body we can use as a i  var

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In your new code   int func int  B        B 0    5      B is a pointer to int  thus B 0  is an int  and you can t dereference an int  Just remove the     int func int  B       B 0    5      and it works   In the initialisation  int B 10     NULL     you are initialising anint with a void   NULL   Since there is a valid conversion from void  to int  that works  but it is not quite kosher  because the conversion is implementation defined  and usually indicates a mistake by the programmer  hence the compiler warns about it   int B 10     0     is the proper way to 0-initialise an int 10

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Maybe you were trying to do this    include  lt stdio h gt   int func int   B           B   OFFSET   5    You are pointing to the same region as B OFFSET           B   2    5     int main void         int B 10        func B           Let s say you edited only 2 and you want to show it         printf  b 0     d n n   B 2         return 0

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main         int  arr 5       int i 31  j 5  k 19  l 71  m       arr 0   amp i      arr 1   amp j      arr 2   amp k      arr 3   amp l      arr 4   amp m       for m 0  m lt  4  m                  printf   d    arr m               return 0

[c] C pass int array pointer as parameter into a function

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