What is Call by Value in C?

In C programming, there are two ways to pass arguments to a function: call by value and call by reference.

Call by value means that the function receives a copy of the value of the variable passed as an argument. In other words, the function works with a local copy of the variable’s value and cannot modify the original value of the variable in the calling function.

Example:

#include <stdio.h>

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

int main() {
    int x = 10, y = 20;
    swap(x, y);
    printf("x = %d, y = %d", x, y); // x = 10, y = 20
    return 0;
}

Output:

x = 10, y = 20

Explanation:

In the above example, the function swap receives the values of x and y as arguments. However, it only works with local copies of these values and cannot modify the original values of x and y in the main function.

Some rules to note:

1. In the called function, the parameters are local variables that are initialized with the values of the corresponding arguments passed in the calling function.
2. Any changes made to the values of the parameters within the called function do not affect the original values of the arguments in the calling function.
3. Call by value is preferred when the values of the arguments passed to the function are not intended to be changed by the function.
4. Complex data structures such as arrays, structures or pointers can be passed by value, but they can be inefficient for large data structures.

What is Call by Reference in C?

#include <stdio.h>

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

int main() {
    int x = 10, y = 20;
    swap(&x, &y);
    printf("x = %d, y = %d", x, y); // x = 20, y = 10
    return 0;
}

Output:

x = 20, y = 10

Explanation:

In the above example, the function swap receives pointers to x and y as arguments. It then dereferences these pointers to modify the original values of x and y in the main function.

Some rules to note:

1. In the called function, the parameters are pointers that are initialized with the memory addresses of the corresponding arguments passed in the calling function.
2. Any changes made to the values of the parameters within the called function affect the original values of the arguments in the calling function.
3. Call by reference is preferred when the values of the arguments passed to the function need to be changed by the function.
4. The caller function needs to ensure that the address of the variable is passed to the function using the “&” operator before the variable’s name.
5. The called function needs to ensure that the pointers are dereferenced using the “*” operator to access the value of the pointed-to variable.
6. Care must be taken to avoid unintended side effects such as modifying the values of the parameters in the called function that can affect the operation of the calling function.
7. Complex data structures such as arrays, structures, or pointers are usually passed by reference to avoid the overhead of copying large amounts of data.

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