C program to Remove Duplicate Characters in a string

Strings are actually one-dimensional array of characters terminated by a null character ‘\0’. Thus a null-terminated string contains the characters that comprise the string followed by a null.

String is a sequence of characters. char data type is used to represent one single character in C. So if you want to use a string in your program then you can use an array of characters.

The declaration and definition of the string using an array of chars is similar to declaration and definition of an array of any other data type.

Any string ends with a terminating null character ‘\0’. An array definition in such a way should include null character ‘\0’ as the last element.

Here is source code of the C program to Remove Duplicate Characters in a string. The C program is successfully compiled and run(on Codeblocks) on a Windows system. The program output is also shown in below.

SOURCE CODE : :

/*  C program to Remove Duplicate Characters in a string  */

#include <stdio.h>

#define MAX_SIZE 100 //Maximum size of the string


/* Function declarations */
void removeDuplicates(char * string);
void removeAll(char * string, const char toRemove, int index);




int main()
{
    char string[MAX_SIZE];

    /* Reads string from user */
    printf("\nEnter any string: ");
    gets(string);

    printf("\nString before removing duplicates: %s\n", string);

    removeDuplicates(string);

    printf("\nString after removing duplicates: %s\n", string);

    return 0;
}




/**
 * Removes all duplicate characters from the given string
 */
void removeDuplicates(char * string)
{
    int i = 0;

    while(string[i] != '\0')
    {
        /* Remove all duplicate of character string[i] */
        removeAll(string, string[i], i);
        i++;
    }
}



/**
 * Removes all occurrences of a given character from string
 * after the given index.
 */
void removeAll(char * string, const char toRemove, int index)
{
    int i, j;

    i = index + 1;

    while(string[i] != '\0')
    {
        /* If duplicate character is found */
        if(string[i] == toRemove)
        {
            /*
             * Shift all characters from current position to one place left
             */
            j = i;
            while(string[j] != '\0')
            {
                string[j] = string[j + 1];
                j++;
            }
        }

        i++;
    }
}

Output:

/*  C program to Remove Duplicate Characters in a string  */

Enter any string: Hello CodezClub

String before removing duplicates: Hello CodezClub

String after removing duplicates: Helo Cdzub

Process returned 0

Above is the source code for C program to Remove Duplicate Characters in a string which is successfully compiled and run on Windows System.The Output of the program is shown above .