Parameter Passing Methods

PARAMETERS PASSING METHODS

In 'C' language, there are two ways that the parameters can be passed to a function, they are

i) Call by value

ii) Call by reference

1. CALL BY VALUE

This method copies the values of actual parameters into the formal parameters of the function. Here, the changes of the formal parameters cannot affect the actual parameters, because formal arguments are photocopy of actual arguments. Changes made in the formal arguments are local to the block of the called functions. Once control returns back to the calling function, the changes made disappear.

Example: Find the cube of given value.

/* Program to find the cube of given value */

#include <stdio.h>

int cube (int x)

main()

{

         /* Local definition */

         int n=5;

         /* Statements */

         printf("Cube of %d is..%d", n,cube(n));

} /* main */

int cube(int);  /* cube is a function to cubic the values */

{

         x=x*x*x;

         return(x);

} /* cube */

OUTPUT

Cube of 5 is.. 125

EXPLANATION: In this example, the value of argument to the function cube(), is copied to the parameter 'x'. The expression x= x*x*x is evaluated, and only the local variable 'x' is modified. The main program print the value of n and transfers the control to called function cube() and calling program get back the values from the called program cube(). The function cube() executes the block of statement and return the values to the main function.

2. CALL BY REFERENCE

Call by Reference is another way of passing parameters to the function. Here, the address of arguments are copied into the parameters inside the function, the address is used to access the actual arguments used in the call. Hence changes made in the arguments are permanent.

Here pointers are passed to function, just like any other arguments. Here, we need not declare the parameters as pointer type.

Example: Interchanging two values.

 /* Program to interchanging two values */

#include <stdio.h>

void interchange (int *a,int *b); /* Prototype declaration */

void main()

{

/* Local definition */

int i=5,j=10;

/* Statements */

clrscr();

printf("i and j values before interchange: %d %d\n",i,j);

interchange(&i,&j); /* pass address to function */

printf("i and j values after interchange : %d %d\n",i,j);

printf("i and j values after interchange in the main(): %d %d\n",i,j);

getch();

} /* main */

void interchange(int *a, int *b)

{

int t;

t=*a;

*a= *b;

*b=t;

} /* interchange */

OUTPUT

i and j values before interchange: 5 10

i and j values after interchange : 10 5

i and j values after interchange in the main(): 10 5

EXPLANATION: In this example, the variables i and j are assigned to values 5 and 0 respectively, then the interchange() function is called with the address of i and j and it interchanges the i and j values. In the program, we are passing addresses of formal arguments to the interchange() function. The pointers in the interchange() function operate on the actual argument through the pointer. So the changes made in the values are permanent.