C Pointers and Functions

C Pointers & Functions

In C, pointers allow functions to directly modify variable values by passing their memory addresses — this is called call by reference. It’s super useful when you want a function to change the actual variables from the calling function.

Passing Pointers to Functions

Instead of passing a value, you pass the address of the variable. The function then uses a pointer to access or modify that value.

Example: Swap Two Numbers Using Pointers

This example uses pointers to swap two numbers from inside a function.

#include <stdio.h>

void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

int main() {
    int x = 10, y = 20;

    printf("Before swap: x = %d, y = %d\n", x, y);
    swap(&x, &y);
    printf("After swap: x = %d, y = %d\n", x, y);

    return 0;
}
  

Explanation

• &x and &y send the address of x and y to the function.
• *a and *b let the function access and modify the actual values.
• This is why x and y change even outside the swap() function!

Why Use Pointers in Functions?

• Efficiently pass large data structures (like arrays).
• Allow functions to return multiple values.
• Modify original variables from within the function.

Practice Challenge

Write a function that receives two float pointers and multiplies them. Then print the result inside and outside the function!

Summary

• Pointers let functions access memory directly.
• Use *ptr to dereference and modify the value.
• Call by reference is done using pointers!