Call by Value in C: Simple Explanation


2 min read

Imagine you're hosting a party and want to share delicious cookies with your friends. You bake a batch of cookies and prepare plates for everyone. However, to avoid running out or giving away the only batch, you decide to make copies of your cookies for each plate.

In programming terms, this is analogous to call by value. When you call a function in C, the values of the arguments you pass (actual arguments) are copied into separate variables within the function (formal arguments). These copies are like the cookie plates, distinct from the original cookie batch you keep.

Key Points:

  • Changes to formal arguments within the function do not affect the original actual arguments. Just like your friends eating cookies from their plates wouldn't affect the original batch.

  • This ensures that the function can't unintentionally modify your original data. It's like having a safe backup of your cookies in case someone accidentally spills juice on a plate.

  • Call by value is useful when you don't want the function to modify the original data. This is often the case when working with sensitive data or when you need to preserve the original values for later use.


      void swap_values(int x, int y) { // Formal arguments
          int temp = x; // Copy of x
          x = y;      // Assign y's value to the copy
          y = temp;    // Assign the copy of x (now y's original value) to y
      int main() {
          int a = 5, b = 10; // Actual arguments
          swap_values(a, b);   // Pass copies to the function
          printf("a is now %d, b is now %d\n", a, b); // Output: a is 5, b is 10

    In this example, the swap_values function doesn't modify the original values of a and b even though it seems to swap them within the function. It only swaps the copies.

    Additional Notes:

    • While call by value is often the default, C also supports call by reference using pointers.

    • Call by value can be less efficient for large data structures because copies are made.

    • Understanding call by value is crucial for writing clear and predictable functions in C.

I hope this explanation is helpful! Feel free to ask if you have any further questions.

Did you find this article valuable?

Support SAHIL ALI by becoming a sponsor. Any amount is appreciated!