C-and-C++/C3/Strings/English

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Title of script: Strings

Author: Ashwini R Patil

Keywords: Strings in C, getline, Video Tutorial


Visual Cue Narration
Slide 1 Welcome to the spoken-tutorial on Strings in C and C++
Slide 2

Learning Objectives

In this tutorial, we will learn,
  • What is a string.
  • Declaration of a string.
  • Initialization of a string.
  • Few examples on string.

We will also see some common errors and their solutions.

Slide 3

System Requirements

To record this tutorial, I am using
  • Ubuntu Operating System version 11.04
  • gcc and g++ Compiler version 4.6.1
Slide 4

Introduction to strings

Let us start with the introduction to strings.

String is a sequence of characters, that is treated as a single data item.

Size of string = length of string + 1

Slide 5

Declaration of the String

Syntax:

char val[10];

Let me tell you how to declare a string.

The syntax for this is

char name_of_string[size];

char, name of string and size

char is the data type, name of the string is the string-name, and we can give the size here.

Eg: here we have declared a character string names with size 10

Please open the Terminal Now we will see an example.

I have already typed the program, so I will open it.

Note that our file name is string.c

In this program, we will take a string as an input from the user and print it.

Let me explain the code now.

Highlight

#include<string.h>

These are our header files.

Here string.h includes the declarations, functions, constants of string handling utilities.

Whenever we work on string functions, we should include this header file.

Highlight

char strname[30];

This is our main function.

Here we are declaring the string strname' with size '30'.

Highlight

printf("Enter the string\n");

Here we are accepting a string from the user.
Highlight

scanf("%[^\n]s",strname);

To read a string, we can use scanf() function with format specifier %s

We are using the caret sign and \n to include the spaces with the string.

Type:

printf("The string is %s\n", strname);

Then we print the string.

And this is our return statement.

Save the program Now click on Save
Execution of the program

On the terminal

Let us execute the program.

Please open the terminal window by pressing Ctrl, Alt and T keys simultaneously on your keyboard.

Type

gcc strdeclare.c str

>> press Enter

To compile, type

gcc space string.c space -o space str

And press Enter

Type

./str

>> press Enter

To execute, type

./str

now press Enter

Here it is displayed as Enter the string .
Type

Talk To A Teacher >> press Enter

I will type Talk To A Teacher.

now press Enter.

Highlight

Output

The output is displayed as The string is Talk To A Teacher
Slide 6


Initialization of the string


Syntax:


char strinitialize[30] = “star”;


(or)


char strinitialize[] = {'S', 't', 'r'};

Now let us switch back to our slides


Until now we discussed about the declaration of a string.

Now we are going to discuss how to initialize the string.

The syntax for this is

char var_name[size] = “string”;

Eg: Here we have declared a character string "names" with size 10 and the string is "Priya"

Another syntax is

char var_name[ ] = {'S', 't', 'r', 'i', 'n', 'g'}; within single quotes

eg: char names[10] = {'P', 'r', 'i', 'y', 'a'}; in single quotes

Please switch to the Text editor Let me show you how to use the first syntax with an example.

Switch back to our Editor. We will use the same example.

Click on File >> Save as option

Type

strinitialize.c

First, press shift, ctrl and s keys simultaneously on your keyboard

Now save the file with the name strinitialize.c

Click on save Now click on Save
Type


char name[30] = "Talk To A Teacher";


We are going to intialize this string.

Hence, on the 5th line, type

= and within double quotes “Spoken- Tutorial”;

Now, click on Save

Delete

printf("Enter the string\n");

scanf("%[^\n]s",strname);

Now remove these two lines, as we are only going to print the string.
Save the program Click on Save.

Let us execute.

On the terminal, type

gcc strinitialize.c -o str1

Come back to our terminal.

To compile, type

gcc space stringintialize.c space -o space str2

To execute

Type

./str1

Here we have str2 because we don't want to overwrite the output parameter str for the file string.c

Now press Enter.

To execute, type ./str2

Highlight

Output

The output is displayed as "The string is Spoken-Tutorial".
Error1

Type

sting.h

Now we will see some common errors which we can come across

Come back to our program

Suppose here we type the spelling of string as

sting

Click on Save Now click on Save.
On the terminal Let us execute; come back to our terminal.
Compile and execute as before


gcc strinitialize.c -o str1


./str1

Now compile as before.

We see an fatal error.

sting.h no such file or directory

compilation terminated

On the editor, correct the spelling Come back to the program.

This is because the compiler is not able to find the header file with the name sting.h

Hence it is giving an error.

Let us fix the error.

Type r here.

Now click on Save.

On the terminal Let us execute again.

Come back to our terminal.

Compile as before, execute as before.

Yes, it is working!

Error2

Type

int

Now, let us see another common error.

Come back to our program.

Suppose, here, I will type int in place of char.

Now, click on Save .

Let us see what happens.

Come back to our terminal.

On the terminal Let me clear the prompt.

Compile as before.

We see an error.

Wide character array initialized from non-wide string

format %s expects argument of type 'char'

But argument 2 has type 'int'


Come back to our program.

This is because we used %s as the format specifier for string.

And we are initializing it with an integer data type int.

On the editor Let us fix the error.

Type char here.

Click on Save.

Let us execute.


On the terminal Come back to our terminal.

Compile as before, execute as before.

Yes it is working!
On the editor NOW WE WILL SEE HOW TO EXECUTE THE SAME PROGRAM IN C++

Come back to our program.

Click on File >> Save as

Type .cpp

Let me open our file string.c

We will edit the code here.

First, press shift, ctrl and S key simultaneously on your keyboard.


Now save the file with an extension .cpp

and click on Save.

Type

iostream

Now we will change the header file as iostream.
Type


#include <string>

Include the using statement.

Now click on Save.

Now we will delete this declaration.

Type

string strname;

And will declare a string variable.

Type string space strname and a semicolon

Click on Save.

Type

cout <<

Replace the printf statement with the cout statement.

Delete the closing bracket here.

Delete scanf statement.

And type

getline opening bracket closing bracket. Within the brackets type(cin, strname);

Delete the scanf statement and type getline opening bracket closing bracket. Within the brackets type(cin, strname)

At the end, type a semicolon.

Type

cout <<"The string is " <<strname <<"\n";


In place of

printf("The string is %s\n",strname);

Now again, replace the printf statement with the cout statement.

Delete the format specifier and \n

Now delete the comma

Type two opening angle brackets, delete the bracket here.

Type two opening angle brackets and within the double quotes type \n

Click on save And click on Save
We have declared a string variable 'strname'

Since we do not use the format specifier in C++, the compiler should know that strname is a string variable.

Here we use getline to extract the characters from the input sequence.

It stores them as a string.

On the terminal Now let us execute the program. Come back to our terminal.
Let me clear the prompt.
Type

g++ string.cpp -o str1

To compile, type

g++ space string.cpp space -o space str3

and press Enter.

Type

./str1

To execute, type

./str3

Press Enter.

Highlight >> type Talk To A Teacher It is displayed as Enter the string

I will enter as Talk To A Teacher

Now press Enter

The output is displayed as

"The string is Talk To A Teacher"

We can see that the output is similar to our C code.

Now come back to our slides.

Slide 7 Let us summarize

In this tutorial we learnt

  • Strings
  • Declaration of a string
  • eg: char strname[30]

  • Initialization of a string
  • eg: char strname[30] = “Talk To A Teacher”

Slide 8

Assignment

As an assignment

Write a program to print a string using the 2nd syntax

Slide 9


About the Spoken Tutorial Project

Watch the video available at the link shown

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 10

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 11


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 signing off.

Thank You for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey

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