C++ LANGUAGE CALL BY VALUE PAGE 72

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C++ LANGUAGE CALL BY VALUE

Call by Value 


The call by value method of passing arguments to 
a function 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. 
By default, C++ uses call by value to pass arguments. In 
general, this means that code within a function cannot alter 
the arguments used to call the function. Consider the function 
swap() definition as follows. 
// 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; 
} 
Now, let us call the function swap() by 
passing actual values as in the following example: 

#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; 
} 
When the above code is put together in a file, 
compiled and executed, it produces the following result:
 
Before swap, value of a :100 
Before swap, value of b :200 
After swap, value of a :100 
After swap, value of b :200 

Which shows that there is no change in the values 
though they had been changed inside the function.