C/C++ Parameter Passing

C parameter passing:-

1. Pass by Value:

- The value of a variable is sent to function.
- The actual parameter cannot be changed by function.
- Duplicate Copy of Original Parameter is Passed.
- No effect on Original Parameter after modifying parameter in function.

#include<stdio.h>

void interchange(int number1,int number2)
{
    int temp;
    temp = number1;
    number1 = number2;
    number2 = temp;
}

int main() {

    int num1=50,num2=70;
    interchange(num1,num2);

    printf("\nNumber 1 : %d",num1);
    printf("\nNumber 2 : %d",num2);

    return(0);
}

2. Pass by Reference:

- An address gets sent to function.
- The function can change the values at that address.
- Actual Copy of Original Parameter is Passed.
- Original Parameter gets affected if value of parameter changed inside function.

#include<stdio.h>

void interchange(int *num1,int *num2)
{
    int temp;
    temp  = *num1;
    *num1 = *num2;
    *num2 = temp;
}

int main() {

    int num1=50,num2=70;
    interchange(&num1,&num2);

    printf("\nNumber 1 : %d",num1);
    printf("\nNumber 2 : %d",num2);

    return(0);
} 

Source:
http://www.c4learn.com/c-programming/c-function-parameter-passing/
http://www.cs.usfca.edu/~wolber/SoftwareDev/C/paramPassing.htm


C++ parameter passing:-

1. Pass by Value:

This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument.

// function definition to swap the values.
void swap(int x, int y) {
   int temp;

   temp = x; /* save the value of x */
   x = y;    /* put y into x */
   y = temp; /* put x into y */
  
   return;
}

#include <iostream>
using namespace std;
 
// function declaration
void swap(int x, int y);
 
int main () {
   // local variable declaration:
   int a = 100;
   int b = 200;
 
   cout << "Before swap, value of a :" << a << endl;
   cout << "Before swap, value of b :" << b << endl;
 
   // calling a function to swap the values.
   swap(a, b);
 
   cout << "After swap, value of a :" << a << endl;
   cout << "After swap, value of b :" << b << endl;
 
   return 0;
} 

2. Pass by Reference:

This method copies the reference of an argument into the formal parameter. Inside the function, the reference is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument.

// function definition to swap the values.
void swap(int &x, int &y) {
   int temp;
   temp = x; /* save the value at address x */
   x = y;    /* put y into x */
   y = temp; /* put x into y */
  
   return;
}

#include <iostream>
using namespace std;

// function declaration
void swap(int &x, int &y);

int main () {
   // local variable declaration:
   int a = 100;
   int b = 200;
 
   cout << "Before swap, value of a :" << a << endl;
   cout << "Before swap, value of b :" << b << endl;

   /* calling a function to swap the values using variable reference.*/
   swap(a, b);

   cout << "After swap, value of a :" << a << endl;
   cout << "After swap, value of b :" << b << endl;
 
   return 0;
} 

3. Pass by Pointer:

This method copies the address of an argument into the formal parameter. Inside the function, the address is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument.

// function definition to swap the values.
void swap(int *x, int *y) {
   int temp;
   temp = *x; /* save the value at address x */
   *x = *y; /* put y into x */
   *y = temp; /* put x into y */
  
   return;
}

#include <iostream>
using namespace std;

// function declaration
void swap(int *x, int *y);

int main () {
   // local variable declaration:
   int a = 100;
   int b = 200;
 
   cout << "Before swap, value of a :" << a << endl;
   cout << "Before swap, value of b :" << b << endl;

   /* calling a function to swap the values.
      * &a indicates pointer to a ie. address of variable a and 
      * &b indicates pointer to b ie. address of variable b.
   */
   swap(&a, &b);

   cout << "After swap, value of a :" << a << endl;
   cout << "After swap, value of b :" << b << endl;
 
   return 0;
}

Source:

https://www.tutorialspoint.com/cplusplus/cpp_functions.htm

http://www.cplusplus.com/articles/z6vU7k9E/