C-and-C++/C4/Function-Call/English

Title of script: Functions in C and C++

Author: Ashwini R. Patil

Keywords: Functions, call by value, call by reference, Video Tutorial

Visual Cue	Narration
Slide 1	Welcome to the spoken tutorial on Function call in C and C++
Slide 2	In this tutorial we will learn function, call by value. call by reference. We will do this through an example.
Slide 3	To record this tutorial, I am using Ubuntu Operating system version 11.10 gcc and g++ Compiler version 4.6.1 on Ubuntu
Slide 4	Let us start with the introduction to functions call by value 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.
	Let us see a program on function call by value. I have already typed the program on the editor. So i will just open it.
Point the cursor to callbyval.c	Please note that our filename is callbyval.c Let me explain the code now. In this program we will calculate the cube of a number.
Highlight #include <stdio.h>	This is our header file
Highlight int cube(int x) { x=x*x*x; return(x); }	Here we have function cube having an argument as x. In this we calculate the cube of x and return the value of x.
Highlight int main()	This is our main function.
Highlight int n=8;	Here we give the value of n as 8.
Highlight printf("Cube of %d is %d\n",n,cube(n));	Then we call the function cube. And print the valu of n and the cube of n.
Highlight return 0;	This is our return statement.
	Now click on Save Now let us execute the program.
Press Ctrl, Alt and T keys simultaneously	Please open the terminal window by pressing Ctrl, Alt and T keys simultaneously
Type gcc callbyval.c -o val Type ./val	To compile the program, type gcc callbyval.c -o val To execute, type ./val
Highlight Output	We see the output is displayed as Cube of 8 is 512.
	Now we will see function call by reference. Let us go back to our slides.
Slide 5	It is another method of passing arguments to the function. 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.
On the editor	Let us see an example on function call by reference. I have already typed the code on the editor. Lets take a look.
Point to the filename callbyref.c	Note that our filename is callbyref.c Let me explain the code now.
Highlight #include<stdio.h>	This is our headerfile as stdio.h
Highlight int swap(int *a, int *b)	Then we have function swap You can see that the arguments passed in the function are pointer type.
Highlight int t; t=*a; *a=*b; *b=t;	Here we have declared an integer variable 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.
Highlight int main()	This is our main function.
Highlight int i, j;	Here we have declared two integer variables as i and j.
Highlight printf("Enter the values "); scanf("%d%d",&i,&j);	Then we take the values of i and j as user inputs. &i and &j will give the memory address of i and j.
Highlight printf("Before swapping %d and %d\n",i,j);	First we print the values before swapping.
Highlight swap(&i,&j);	Here we call the function swap
Highlight printf("After swapping %d and %d\n",i,j);	Now we print the values after swapping.
Highlight return 0;	This is our return statement.
Click on Save	Click on Save
On the terminal	Let us execute the program Come back to our terminal
Type gcc callbyref.c -o ref Type ./ref	Now compile the program as before, gcc callbyref.c -o ref let us execute ./ref
Highlight Output	We see it is output is displayed as: Enter the values I will enter as 6 and 4 Before swapping 6 and 4 After swapping 4 and 6
	NOW LET US SEE HOW TO EXECUTE THE SAME PROGRAM IN C++ I have the code, lets go through it.
Point cursor callbyref.cpp	Note that our filename is callbyref.cpp Let me explain the code now.
Type <iostream>	First we will change the header file <iostream>
Type using namespace std;	We have used the std namespace
Highlight int swap(int &x, int &y) { int temp; temp = x; x = y; y = temp; }	The function declaration is same in C++. 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.
Highlight The code	Rest of the code is similar to our C code. The printf and scanf statement is replaced by cout and cin statement.
On the terminal	Let us compile the program Come back to the terminal
Type g++callbyref.cpp -o ref1 Type ./ref1	Type g++callbyref.cpp -o ref1 press Enter To execute Type ./ref1
Highlight Output	Here it is displayed as: Enter values of a and b I will enter 4 3 The output is displayed as Before swapping a and b: 4 and 3 After swapping a and b: 3 and 4
	This brings us to the end of this tutorial. Let us go back to our slides.
Slide 6	Let us summarize, In this tutorial we learn't: Function call by value. Function call by reference.
Slide 7 Assignment	As an assignment Write a similar program to calculate the cube of a number. Using call by value in C++.
Slide 8 About the Spoken Tutorial Project	Watch the video available at http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial It summarises the Spoken Tutorial project If you do not have good bandwidth, you can download and watch it
Slide 9 Spoken Tutorial Workshops	The Spoken Tutorial Project Team Conducts workshops using spoken tutorials Gives certificates to those who pass an online test For more details, please write to contact@spoken-tutorial.org
Slide 10 Acknowledgement	Spoken Tutorial Project is a part of the Talk to a Teacher project It is supported by the National Mission on Education through ICT, MHRD, Government of India More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro
	This is Ashwini Patil from IIT Bombay Thank You for joining

Contributors and Content Editors

Ashwini, Sneha