Question

I would just like to confirm that when I have a function of the sort

int subtract(int a, int b)
{
return a-b;
}

I am passing values when i call subtract(3,2) rather than pointers.

Thanks,

Answer 1

Yes you are

• a parameter of type int a means pass an integer by value to the function
• a parameter of type int* a means pass a a pointer to some integer to the function.

so for this

int subtract(int a, int b) 
{ 
   // even if I change a or b  in here - the caller will never know about it....
   return a-b; 
} 

you call like this:

int result  = substract(2, 1); // note passing values

for pointers

int subtract(int *a, int *b) 
{ 
   // if I change the contents of where a or b point the  - the caller will know about it....
   // if I say *a = 99;  then x becomes 99 in the caller (*a means the contents of what 'a' points to)
   return *a - *b; 
} 

you call like this:

int x = 2;
int y = 1;
int result  = substract(&x, &y); // '&x means the address of x' or 'a pointer to x'