Call by Value and Call by Reference in C

Call by Value

In C, In call by value, a copy of the argument is passed to the function. Any modifications made to the argument within the function do not affect the original value outside the function.

Example:

void swap_values(int x, int y) {
    int temp = x;
    x = y;
    y = temp;
}

int main() {
    int a = 10, b = 20;
    swap_values(a, b);
    printf("a = %d, b = %dn", a, b); // Output: a = 10, b = 20
    return 0;
}

In this example, swap_values is called by value, so the original values of a and b remain unchanged.

Call by Reference

In call by reference, the address of the argument is passed to the function. This allows the function to modify the original value.

Example:

void swap_references(int *x, int *y) {
    int temp = *x;
    *x = *y;
    *y = temp;
}

int main() {
    int a = 10, b = 20;
    swap_references(&a, &b);
    printf("a = %d, b = %dn", a, b); // Output: a = 20, b = 10
    return 0;
}

In this example, swap_references is called by reference, so the original values of a and b are swapped.

Key Differences: Call by Value vs Call by Reference

Difference Between Call By Value and Call By Reference

When to Use Which:

• Use call by value for simple data types when you don’t need to modify the original value within the function.
• Use call by reference when you need to modify the original value of a variable within a function. This is often used for passing large data structures or modifying global variables.

Call By Reference. While calling a function, we pass values of variables to it. Such functions are known as “Call By Values”. While calling a function, instead of passing the values of variables, we pass address of variables(location of variables) to the function known as “Call By References.