C Program to Replace First Occurrence of a Character in a String

In this article, we will show you, How to write a C Program to Replace First Occurrence of a Character in a String with example.

C Program to Replace First Occurrence of a 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 search and replace the first occurrence of a character inside a string.

/* C Program to Replace First Occurrence of a Character in a String */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100], ch, Newch;
  	int i;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	printf("\n Please Enter the Character that you want to Replace :  ");
  	scanf("%c", &ch);
  	
  	getchar();
  	
  	printf("\n Please Enter the New Character :  ");
  	scanf("%c", &Newch);
  	
  	for(i = 0; str[i] != '\0'; i++)
  	{
  		if(str[i] == ch)  
		{
  			str[i] = Newch;
  			break;
 		}
	}
	printf("\n The Final String after Replacing First occurrence of '%c' with '%c' = %s ", ch, Newch, str);
	
  	return 0;
}

OUTPUT

ANALYSIS

First we used For Loop to iterate each and every character in a String.

for(i = 0; i <= strlen(str); i++)
{
	if(str[i] == ch)  
	{
		str[i] = Newch;
		break;    	
	}
}

str[] = Hello World
ch = l
Newch = @

For Loop First Iteration: for(i = 0; i <= strlen(str); i++)
Within the While Loop we used If Statement to check whether the str[0] is equal to user specified character or not
if(str[i] == ch) => if(H == l)
Above condition is false. So, i value will be incremented, and Flag is still 0.

Second Iteration: for(i = 1; 1 <= 11; 1++)
if(str[i] == ch) => if(e == l)
Above condition is false. So, i value will be incremented, and Flag is still 0.

Third Iteration: for(i = 2; 2 <= 11; 2++)
if(str[i] == ch) => if(l == l)
Above condition is True.
str[i] = Newch
str[2] = @
and, break statement will exit from the loop

Next, we used the printf statement to print the final string.

printf("\n The Final String after Replacing First occurrence of '%c' with '%c' = %s ", ch, Newch, str);

C Program to Replace First Occurrence of a Character in a String Example 2

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

/* C Program to Replace First Occurrence of a Character in a String */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100], ch, Newch;
  	int i = 0;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	printf("\n Please Enter the Character that you want to Replace :  ");
  	scanf("%c", &ch);
  	
  	getchar();
  	
  	printf("\n Please Enter the New Character :  ");
  	scanf("%c", &Newch);
  	
  	while(i <= strlen(str))
  	{
  		if(str[i] == ch)  
		{
  			str[i] = Newch;
  			break;
 		}
 		i++;
	}
	printf("\n The Final String after Replacing First occurrence of '%c' with '%c' = %s ", ch, Newch, str);
	
  	return 0;
}

OUTPUT

C Program to Replace First Occurrence of a 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 Replace First Occurrence of a Character in a String */
 
#include <stdio.h>
#include <string.h>

void Replace_FirstOccurrence(char *str, char ch, char Newch);
 
int main()
{
  	char str[100], ch, Newch;
  	int i = 0;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	printf("\n Please Enter the Character that you want to Replace :  ");
  	scanf("%c", &ch);
  	
  	getchar();
  	
  	printf("\n Please Enter the New Character :  ");
  	scanf("%c", &Newch);
  	
  	Replace_FirstOccurrence(str, ch, Newch);
  	
  	printf("\n The Final String after Replacing First occurrence of '%c' with '%c' = %s ", ch, Newch, str);
	
  	return 0;
}

void Replace_FirstOccurrence(char *str, char ch, char Newch)
{
	int i;

	for(i = 0; str[i] != '\0'; i++)
	{
		if(str[i] == ch)
		{
			str[i] = Newch;
  			break;
		}  
	}
}

OUTPUT

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