Pointers and variables assignment basic

Question

I'm trying to understand the basic of pointers, and done this code:

int c = 3;
int try(int a){
  ++a;
  return 0;
}
int main(){
  try(c);
  printf("%d\n",c);
  return 0;
}

How do I manage to print 4 with pointers? I know that I can do it like this:

int c = 3;
int try(int a){
  ++a;
  return a;
}
int main(){
  c = try(c);
  printf("%d\n",c);
  return 0;
}

but I really want to learn how to pass those values through functions via pointers.

Furthermore, any great book recommendation for solid C learning is always welcome. Thanks in advance.

It may be a poor choice to name a function try. While it is valid in C, it happens to be a C++ keyword, and can cause confusion. — abelenky
– abelenky, Commented Apr 27, 2022 at 16:27

abelenky · Accepted Answer · 2022-04-27 16:30:52Z

1

int c = 3;


void pass_by_ref(int *a)  // Take a Pointer to an integer variable
{
    ++(*a);               // Increment the value stored at that pointer.
}

int main(){
  pass_by_ref(&c);        // Pass the address of the variable to change
  printf("%d\n",c);
  return 0;
}

answered Apr 27, 2022 at 16:30

abelenky

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Comments

pm100 · Accepted Answer · 2022-04-27 16:34:10Z

0

This is how to do 'c style pass by reference'

int tryIt(int *a){
  ++(*a);
}
int main(){
  int c = 3;
  tryIt(&c);
  printf("%d\n",c);
  return 0;
}

You pass a pointer to the variable and the dereference the pointer in the function. The function effectively 'reaches out ' of its scope to modify the passed variable

Note that I moved c into main. In your original code 'try' could have modified c itself since its at global scope.

And changed 'try' to 'tryIt' - cos that looks weird

answered Apr 27, 2022 at 16:34

pm100

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1 Comment

nb0me Over a year ago

Thanks! This is what I was looking for. PS: The "try" was a translation from my language to post here in English lol.

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