Types of Parameter Passing Techniques in Functions

In C, function parameters can be passed to functions in two ways:

1. Call by Value (Pass by Value)

2. Call by Reference (Pass by Address or Pointer)

   

1. Call by Value (Pass by Value)

• A copy of the actual parameter is passed to the function.
• Any changes made inside the function do not affect the original value in the calling function.
• It is safe since the original variable remains unchanged.

Example of Call by Value:

#include <stdio.h>

void changeValue(int x) { 

   x = 100;  // Change the value of x

   printf("Inside function: x = %d\n", x);

}

int main() {

   int num = 50;

   printf("Before function call: num = %d\n", num);

   changeValue(num);  // Function call (pass by value)

   printf("After function call: num = %d\n", num);

   return 0;

}

Output:

Before function call: num = 50 

Inside function: x = 100 

After function call: num = 50 

Explanation:

• The function changeValue() receives a copy of num.
• Inside the function, the value changes to 100, but this change does not reflect in main().
• This proves that the original variable remains unchanged.

2. Call by Reference (Pass by Address or Pointer)

• Instead of passing a copy, the actual memory address (reference) of the variable is passed.
• Changes made inside the function directly modify the original variable.
• This is useful for modifying values and working with large data structures (e.g., arrays).

Example of Call by Reference:

#include <stdio.h>

void changeValue(int *x) { 

   *x = 100;  // Modify the value at the memory address

   printf("Inside function: *x = %d\n", *x);

}

int main() {

   int num = 50;

   printf("Before function call: num = %d\n", num);

   changeValue(&num);  // Function call (pass by reference)

   printf("After function call: num = %d\n", num);

   return 0;

}

Output:

Before function call: num = 50 

Inside function: *x = 100 

After function call: num = 100 

Explanation:

• The function changeValue() receives the address of num using a pointer (int *x).
• Modifying *x directly affects the original num in main().
• The value is changed permanently because we are working with the actual memory location.

Key Differences Between Call by Value and Call by Reference

• Call by Value is used when we do not want the function to modify the original data.
• Call by Reference is used when we want the function to modify the original variable.
• In C, arrays are always passed by reference because their base address is passed automatically.