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 calls in C and C++
Slide 2	In this tutorial we will learn about type of function calls namely, 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
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. I will just open it.
Point the cursor to callbyval.c	Please note that our filename is callbyval.c In this program we will calculate the cube of a number. Let me explain the code now.
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 int x. In this function 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. n is an integer variable.
Highlight printf("Cube of %d is %d\n",n,cube(n));	Then we call the function cube. And print the value of n and the cube of n.
Highlight return 0;	And this is our return statement.
	Now let us execute the program.
Press Ctrl, Alt and T keys simultaneously	open the terminal window by pressing Ctrl, Alt and T keys simultaneously on your keyboard.
Type gcc callbyval.c -o val Type ./val	To compile type gcc space callbyval.c space -o space val Press Enter Now type ./val Press Enter
Highlight Output	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.
Point to the filename callbyref.c	Note that our filename is callbyref.c
Highlight #include<stdio.h>	This is our headerfile as stdio.h
Highlight int swap(int *a, int *b)	Then we have function swap 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.
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. Like this the values are exchanged.
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);	Then we call the function swap
Highlight printf("After swapping %d and %d\n",i,j);	And then we print the values after swapping.
Highlight return 0;	And this is our return statement.
On the terminal	Now let us execute the program Switch back to our terminal
Type gcc callbyref.c -o ref Type ./ref	To compile type, gcc space callbyref.c space -o space ref Press Enter Now type ./ref Press Enter
Highlight Output	We see: 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
	NOW LET US SEE HOW TO EXECUTE THE SAME PROGRAM IN C++ I have the code, lets go through it.
Point cursor callbyref.cpp	This is the second program function callbyreference Note that our filename is callbyref.cpp Let us go through the code.
Type <iostream>	This is our header file as <iostream>
Type using namespace std;	Here we are using 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 statement is replaced by cout and the scanf statement is replaced by cin
On the terminal	Now let us execute the program Come back to our terminal
Type g++ callbyref.cpp -o ref1 Type ./ref1	To compile type g++ space callbyref.cpp space -o space ref1 press Enter Now type ./ref1 press Enter
Highlight Output	Here it is displayed as: 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
	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. And 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 the link shown below. 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 the link shown below: http://spoken-tutorial.org\NMEICT-Intro
	This is Ashwini Patil from IIT Bombay Thank You for joining

Contributors and Content Editors

Ashwini, Sneha