C Program to Remove All Duplicate Character in a String

In this article, we will show you, How to write a C Program to Remove All Duplicate Character in a String with example.

C Program to Remove All Duplicate Character in a String Example 1

This program allows the user to enter a string (or character array), and a character value. Next, it will find and remove all duplicate characters inside a string.

/* C Program to Remove All Duplicate Character in a String */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100];
  	int i, j, k;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	 	
  	for(i = 0; i < strlen(str); i++)
  	{
  		for(j = i + 1; str[j] != '\0'; j++)
  		{
  			if(str[j] == str[i])  
			{
  				for(k = j; str[k] != '\0'; k++)
				{
					str[k] = str[k + 1];
				}
 			}
		}
	}
	
	printf("\n The Final String after Removing All Duplicates = %s ", str);
	
  	return 0;
}

OUTPUT

ANALYSIS

Here, we used For Loop to iterate each and every character in a String, and remove all the duplicate characters in it..

for(i = 0; i < strlen(str); i++)
{
	for(j = i + 1; str[j] != '\0'; j++)
	{
		if(str[j] == str[i])  
		{
			for(k = j; str[k] != '\0'; k++)
			{
				str[k] = str[k + 1];
			}
		}
	}
}

str[] = helloh
ch = l

First For Loop – First Iteration: for(i = 0; i < strlen(str) ; i++)
The condition is True because 0 < 6.
Next, it will enter into Second For Loop

Second For Loop – First Iteration: for(j = i + 1; str[j] != ‘\0’; j++)
=> for(j = 1; e != ‘\0’; 1++)
Within the For Loop we used If Statement to check whether the str[1] is equal to str[0]
if(str[j] == str[i]) => if(e == h)
Above condition is false. So, i value will be incremented.

Second For Loop – Second Iteration: for(j = 2; l != ‘\0’; 2++)
if(str[j] == str[i]) => if(l == h)
Above condition is false. So, i value will be incremented.

Second For Loop – Third Iteration: for(j = 3; l != ‘\0’; 3++)
if(str[j] == str[i]) => if(l == h)
Above condition is false. So, i value will be incremented.

Second For Loop – Fourth Iteration: for(j = 4; o != ‘\0’; 4++)
if(str[j] == str[i]) => if(o == h)
Above condition is false. So, i value will be incremented.

Second For Loop – Fifth Iteration: for(j = 5; h != ‘\0’; 5++)
if(str[j] == str[i]) => if(h == h)
Above condition is True. So, it will enter into third For Loop

Third For Loop – First Iteration: for(k = j; str[k] != ‘\0’; k++)
=> for(k = 5; str[5] != ‘\0’; 5++)
str[k] = str[k + 1];
str[k] = ‘\0’

Third For Loop – Second Iteration: for(k = 6; ‘\0’ != ‘\0’; 6++)
Condition fails. So, it will exit from the Third For Loop.

Do the same for remaining iterations

At last we used the printf statement to print the final string

printf("\n The Final String after Removing All Duplicates = %s ", str);

C Program to Remove All Duplicate Character in a String Example 2

This program is same as above. Here, we just replaced the For Loop with While Loop. I suggest you to refer While Loop to understand the Loop iterations.

/* C Program to Remove All Duplicate Character in a String */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100];
  	int i, j, k;
  	i = 0;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	 	
  	while(i < strlen(str))
  	{
  		j = i + 1;
  		
  		while(str[j] != '\0')
  		{
  			if(str[j] == str[i])  
			{
				k = j;
				
  				while(str[k] != '\0')
				{
					str[k] = str[k + 1];
					k++;
				}
 			}
 			j++;
		}
		i++;
	}
	
	printf("\n The Final String after Removing All Duplicates = %s ", str);
	
  	return 0;
}

OUTPUT

C Program to Remove All Duplicate Character in a String Example 3

This program is same as first example, but this time we used the Functions concept to separate the logic.

/* C Program to Remove All Duplicate Character in a String */
 
#include <stdio.h>
#include <string.h>

void Remove_AllOccurrence(char *str);
 
int main()
{
  	char str[100];
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	 	
  	Remove_AllOccurrence(str);
	
	printf("\n The Final String after Removing All Duplicates = %s ", str);
	
  	return 0;
}

void Remove_AllOccurrence(char *str)
{
	int i, j, k;
	
	for(i = 0; i < strlen(str); i++)
  	{
  		for(j = i + 1; str[j] != '\0'; j++)
  		{
  			if(str[j] == str[i])  
			{
  				for(k = j; str[k] != '\0'; k++)
				{
					str[k] = str[k + 1];
				}
 			}
		}
	}
}

OUTPUT

C Program to Remove All Duplicate Character in a String Example 4

In this program we further divided the code using another function.

/* C Program to Remove All Duplicate Character in a String */
 
#include <stdio.h>
#include <string.h>

void Remove_AllDuplicates(char *str);
void Remove_AllOccurrence(char *str, const char ch, int index);
 
int main()
{
  	char str[100];
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	 	
  	Remove_AllDuplicates(str);
	
	printf("\n The Final String after Removing All Duplicates = %s ", str);
	
  	return 0;
}
// This will remove all the Duplicates
void Remove_AllDuplicates(char *str)
{
	int i;
	
	for(i = 0; i < strlen(str); i++)
  	{
           /* Calling Remove_AllOccurrence function to remove all the occurrence 
           of this particular character */
  		Remove_AllOccurrence(str, str[i], i + 1);  		
	}
}

// This will remove all the Occurrence of any single character
void Remove_AllOccurrence(char *str, const char ch, int index)
{
	int k;
	
	while(str[index] != '\0')
  	{
		if(str[index] == ch)  
		{
  			for(k = index; str[k] != '\0'; k++)
			{
				str[k] = str[k + 1];
			}
 		}
 		index++;
	}
}

OUTPUT

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