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

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

C Program to find 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 find the first occurrence of a character inside a string using If Else Statement.

/* C Program to find First Occurrence of a Character in a String */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100], ch;
  	int i, Flag;
  	Flag = 0;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	printf("\n Please Enter the Character that you want to Search for :  ");
  	scanf("%c", &ch);
  	
  	for(i = 0; i <= strlen(str); i++)
  	{
  		if(str[i] == ch)  
		{
  			Flag++;
			break;    	
 		}
	}
    if(Flag == 0)
  	{
  		printf("\n Sorry!! We haven't found the Search Character '%c' ", ch);
	}
	else
	{
		printf("\n The First Occurrence of the Search Element '%c' is at Position %d ", ch, i + 1);
	}	
  	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)  
	{
		Flag++;
		break;    	
	}
}

str[] = Hello World
ch = l
Flag = 0

Loop First Iteration: for(i = 0; i <= strlen(str); i++)
Within the For 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.
Flag++ means Flag  = 1
and, break statement will exit from the loop

Next, we used the If Else Statement to check the Flag value is equal to 0. Here, the condition is False so, statement inside the else block will be executed.

printf("\n The First Occurrence of the Search Element '%c' is at Position %d ", ch, i + 1);

Here, i is the index position (start with zero), and i + 1 is the actual position.

C Program to find 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 find First Occurrence of a Character in a String */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100], ch;
  	int i, Flag;
  	i = Flag = 0;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	printf("\n Please Enter the Character that you want to Search for :  ");
  	scanf("%c", &ch);
  	
  	while(str[i] != '\0')
  	{
  		if(str[i] == ch)  
		{
  			Flag++;
			break;    	
 		}
 		i++;
	}
    if(Flag == 0)
  	{
  		printf("\n Sorry!! We haven't found the Search Character '%c' ", ch);
	}
	else
	{
		printf("\n The First Occurence of the Search Element '%c' is at Position %d ", ch, i + 1);
	}	
  	return 0;
}

OUTPUT

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

int Find_FirstCharcater(char str[], char ch);

int main()
{
  	char str[100], ch;
  	int index;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	printf("\n Please Enter the Character that you want to Search for :  ");
  	scanf("%c", &ch);
  	
  	index = Find_FirstCharcater(str, ch); 
  	
    if(index == -1)
  	{
  		printf("\n Sorry!! We haven't found the Search Character '%c' ", ch);
	}
	else
	{
		printf("\n The First Occurrence of the Search Element '%c' is at Position %d ", ch, index + 1);
	}	
  	return 0;
}

int Find_FirstCharcater(char str[], char ch)
{
	int i;
	
	for(i = 0; str[i] != '\0'; i++)
	{
		if(str[i] == ch)
		{
			return i;
		}  
	}
	return -1;
}

OUTPUT

C Program to find First Occurrence of a Character in a String Example 4

This program is same as the first example, but this time we are using the pointers concept.

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

int Find_FirstCharcater(char *str, char ch);

int main()
{
  	char str[100], ch;
  	int index;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	printf("\n Please Enter the Character that you want to Search for :  ");
  	scanf("%c", &ch);
  	
  	index = Find_FirstCharcater(str, ch); 
  	
    if(index == -1)
  	{
  		printf("\n Sorry!! We haven't found the Search Character '%c' ", ch);
	}
	else
	{
		printf("\n The First Occurrence of the Search Element '%c' is at Position %d ", ch, index + 1);
	}	
  	return 0;
}

int Find_FirstCharcater(char *str, char ch)
{
	int i;
	
	while(*str)
	{
		if(*str == ch)
		{
			return i;
		}
		i++;
		str++;  
	}
	return -1;
}

OUTPUT

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