Computer Programming - Strings

Post By: Hanan Mannan (H.M.R.A Group Engineers)
Contact Number: Pak (+92)-321-59-95-634
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Computer Programming - Strings

During our discussion about characters in computer programming, we learnt that character data type deals with a single character and you can assign any character from your keyboard to a character type variable.

Now, let's move a little bit ahead and consider a situation where we need to store more than one character in a variable. We have seen that C programming does not allow to store more than one character in a character type variable. So following statements are invalid in C programming and produce syntax error:

char ch1 = 'ab';
char ch2 = '10';

We also have seen how we can store more than one value of similar data type in a variable using arrayconcept. If recap then, here is the syntax to store and print 5 numbers in an array of int type:

#include 

main()
{
    int number[5] = {10, 20, 30, 40, 50};
    int i = 0;
        
    while( i < 5 )
    {
        printf("number[%d] = %d\n", i, number[i] );
        i = i + 1;
   }
}

When the above code is compiled and executed, it produces the following result:

number[0] = 10
number[1] = 20
number[2] = 30
number[3] = 40
number[4] = 50

Now, let's define an array of 5 characters in the similar way as we did for numbers and try to print them:

#include 

main()
{
    char ch[5] = {'H', 'e', 'l', 'l', 'o'};
    int i = 0;
        
    while( i < 5 )
    {
        printf("ch[%d] = %c\n", i, ch[i] );
        i = i + 1;
   }
}

Here, we used %c to print character value. When the above code is compiled and executed, it produces the following result:

ch[0] = H
ch[1] = e
ch[2] = l
ch[3] = l
ch[4] = o

If you are done with the above example, then I think you understood about strings in C programming, because strings in C are represented as arrays of characters. C programming simplified the assignment and printing of strings. Let's check same example once again with simplified syntax:

#include 

main()
{
    char ch[5] = "Hello";
    int i = 0;
    
    /* Print as a complete string */
    printf("String = %s\n", ch);  
    
    /* Print character by character */
    while( i < 5 )
    {
        printf("ch[%d] = %c\n", i, ch[i] );
        i = i + 1;
   }
}

Here, we used %s to print full string value using array name ch, which is actually beginning of the memory address holding ch variable as shown below:

Though it's not visible from the above examples, but internally C program assigns null character '\0' as the last character of every string. This indicates the end of the string and it means if you want to store a 5 character string in an array then you must define array size of 6 as a good practice, though C does not complain about it.

Now if the above code is compiled and executed, it produces the following result:

String = Hell
ch[0] = H
ch[1] = e
ch[2] = l
ch[3] = l
ch[4] = o

Basic String Concepts

Based on the above discussion we can conclude the following important points to remember about strings in C programming language:

• Strings in C are represented as arrays of characters.
• We can constitute a string in C programming by assigning character by character into an array of characters.
• We can constitute a string in C programming by assigning a complete string enclosed in double quote.
• We can print a string character by character using array subscript or a complete string by using array name without subscript.
• Though it's not visible from the above examples, but internally C program assigns null character'\0' as the last character of every string. This indicates the end of the string and it means if you want to store a 5-character string in an array then you must define array size of 6 as a good practice, though C does not complain about it.
• Most of the programming languages provide built-in functions to manipulate strings, i.e., you can concatenate strings, you can search from a string, you can take sub string from the string. For a detail you can check detailed tutorial for C or other programming languages.

Strings in Java

Though you can use character array to store strings but Java is an advanced programming language and its designers tried to provide additional functionality like Java provides string as a built-in data type like any other data type. So it means you can define strings directly instead of defining them array of characters.

Following is the equivalent program written in Java programming language. Java programming makes use of new operator to create string variable as shown below in the program:

You can try to execute the following program to see the output:

public class DemoJava
{    
   public static void main(String []args) 
   {
       String str = new String("Hello");  
       
       System.out.println( "String = " + str );
   }
}

When above program is executed, it produces the following result:

String = Hello

Strings in Python

Creating strings in Python is as simple as simply assigning a string into a Python variable using single or double quote as shown below:

Following is a simple program, which creates two strings and print them using print() function:

var1 = 'Hello World!'
var2 = "Python Programming"

print "var1 = ", var1
print "var2 = ", var2

When above program is executed, it produces the following result:

var1 =  Hello World!
var2 =  Python Programming

Python does not support a character type; these are treated as strings of length one, thus also considered a substring.

To access substrings, use the square brackets for slicing along with the index or indices to obtain your substring. Following is a simple example:

var1 = 'Hello World!'
var2 = "Python Programming"

print "var1[0]: ", var1[0]
print "var2[1:5]: ", var2[1:5]

When the above code is executed, it produces the following result:

var1[0]:  H
var2[1:5]:  ytho