Difference between revisions of "C-and-C++/C4/Function-Call/English"

call by value.

call by reference.

We will do this through an example.

Ubuntu Operating system version 11.10

gcc and g++ Compiler version 4.6.1

It is a method of passing arguments to the function.

When we pass a variable by value it makes a copy of the variable.

Before passing to the function.

Changes made to the arguments inside the function will remain in the function.

It will not be affected outside the function.

I have already typed the program on the editor.

I will just open it.

callbyval.c

In this program we will calculate the cube of a number.

Let me explain the code now.
 

#include <stdio.h>

int cube(int x)

{

x=x*x*x;

return(x);

}

In this function we calculate the cube of x and return the value of x.

int main()

int n=8;

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

And print the value of n and the cube of n.

return 0;

Now let us execute the program.

gcc callbyval.c -o val

Type

./val

gcc space callbyval.c space -o space val Press Enter

Now type

./val Press Enter

Output

Cube of 8 is 512.

Let us go back to our slides.

This method copies the address of the argument instead of the value.

Changes made to the arguments inside a function can affect them outside.

In this we need to declare the arguments as pointer type.

callbyref.c

#include<stdio.h>

int swap(int *a, int *b)

This function will exchange the values of the variables. Value of a will be stored in value of b and vice versa.

You can see that the arguments passed in the function are pointer type.

int t;

t=*a;

*a=*b;

*b=t;

First value of *a is stored in t.

Then value of *b is stored in *a.

Then value of t is stored in *b. Like this the values are exchanged.

int main()

int i, j;

printf("Enter the values ");

scanf("%d%d",&i,&j);

&i and &j will give the memory address of i and j.

printf("Before swapping %d and %d\n",i,j);

swap(&i,&j);

printf("After swapping %d and %d\n",i,j);

return 0;

Switch back to our terminal

gcc callbyref.c -o ref

Type

./ref

gcc space callbyref.c space -o space ref Press Enter

Now type

./ref Press Enter

Output

Enter the values

I will enter as 6 and 4

The output is displayed as:

Before swapping 6 and 4

After swapping 4 and 6

I have the code, lets go through it.

callbyref.cpp

Note that our filename is callbyref.cpp

Let us go through the code.

<iostream>

<iostream>

using namespace std;

int swap(int &x, int &y)

{

int temp;

temp = x;

x = y;

y = temp;

}

In this we pass the arguments as &x and &y.

This will give the memory address of x and y.

Here we swap the values.

The code

The printf statement is replaced by cout and the scanf statement is replaced by cin

Come back to our terminal

g++ callbyref.cpp -o ref1

Type

./ref1

g++ space callbyref.cpp space -o space ref1

press Enter

Now type

./ref1 press Enter

Output

Enter values of a and b

I will enter as

4

3

The output is displayed as

Before swapping a and b: 4 and 3

After swapping a and b: 3 and 4

Let us go back to our slides.

Function call by value.

And

Function call by reference.

Assignment

Write a similar program to calculate the cube of a number.

Using call by value in C++.

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