Call by Value and Call by Reference in C

When programming in C, it is important to understand the concepts of “call by value” and “call by reference.” These are two different ways in which arguments can be passed to functions in C, and they have significant implications for how the function operates and how it affects the original data.

Call by Value

In C, when a function is called with arguments passed by value, a copy of the value is made and passed to the function. This means that any changes made to the arguments within the function do not affect the original values outside of the function.

When using call by value, the function works with a copy of the original data, so any modifications made to the parameters within the function are only visible within the function itself. The original values remain unchanged.

Here is an example to illustrate call by value:

#include <stdio.h>

void changeValue(int num) {
    num = 10;
}

int main() {
    int num = 5;
    printf("Before function call: %dn", num);
    changeValue(num);
    printf("After function call: %dn", num);
    return 0;
}

In this example, the function changeValue takes an integer parameter num and assigns it a new value of 10. However, when the function is called in the main function, the original value of num remains unchanged. The output of this program will be:

Before function call: 5
After function call: 5

Call by Reference

Call by reference in C allows a function to modify the original values of variables passed as arguments. Instead of passing a copy of the value, the function receives a reference to the original variable. This means that any changes made to the arguments within the function will affect the original values outside of the function.

When using call by reference, the function works directly with the original data, so any modifications made to the parameters within the function will be reflected in the original values.

Here is an example to illustrate call by reference:

#include <stdio.h>

void changeValue(int *num) {
    *num = 10;
}

int main() {
    int num = 5;
    printf("Before function call: %dn", num);
    changeValue(#);
    printf("After function call: %dn", num);
    return 0;
}

In this example, the function changeValue takes a pointer to an integer num and assigns it a new value of 10 using the dereference operator (*). When the function is called in the main function, the original value of num is modified. The output of this program will be:

Before function call: 5
After function call: 10

Choosing Between Call by Value and Call by Reference

The choice between call by value and call by reference depends on the specific requirements of the program. Call by value is generally used when the function does not need to modify the original values and only requires a copy of the data. On the other hand, call by reference is used when the function needs to modify the original values or when passing large data structures to avoid the overhead of copying.

It is important to note that call by value is the default behavior in C. To pass arguments by reference, pointers must be used to pass the addresses of the variables.

Understanding the difference between call by value and call by reference in C is crucial for writing efficient and effective programs. By choosing the appropriate method, you can ensure that your functions behave as intended and that your data is manipulated correctly.