C Program to Compare Two Strings

How to compare two strings in C?

To compare two strings in C there are 4 ways.

1. Using strcmp() function
2. Using pointers
3. Without using strcmp() function
4. Using macros

1. strcmp() function | C program to compare two strings using strcmp()

strcmp() function compares two strings and returns 0 if they are equal and same, returns a value greater than 0 if first string is greater than second and return a value less than 0 if first string is less than second string.

Here Character by character comparsion takes place by considering the ascii values of characters.

/* Compare two strings using strmp() function */

#include<stdio.h>
#include<string.h>
 
int main()
{
	char str1[100], str2[100];
 
	printf("\n Enter first string:- ");
	gets(a);
 
	printf("\n Enter second string:- ");
	gets(b);
 
	if (strcmp(str1,str2) == 0)
		printf("\n Two strings entered are equal.\n");
	else
		printf("\n The strings are not equal.\n");
 
   return 0;
}

Output

Output of above code:-
Enter first string:- Programming
Enter second string:- Programming
Two strings entered are equal.

2. Using Pointers | C program to compare two strings using pointers

 /* Compare two strings using pointer */

#include<stdio.h>
 
int string_comparison(char*, char*);
 
int main()
{
	char string1[1000], string2[1000]:
	int result;
   
	printf("\n Enter first string:- ");
	gets(string1);
   
	printf("\n Enter second string:- ");
	gets(string2);
   
	result = string_comparison(string1, string2);
   
	if(result == 0)
		printf("\n Two strings entered are same.\n");
	else
		printf("\n The strings entered are different.\n");
       
	return 0;
}
 
int string_comparison(char *string1, char *string2)
{
	while (*string1 == *string2)
	{
		if (*string1 == '\0' || *string2 == '\0')
		break;
         
		string1++;
		string2++;
	}
 
	if (*string1 == '\0' && *string2 == '\0')
		return 0;
	else
		return -1;
}

3. Without using strcmp() | C program to compare two strings without using library functions

We can also compare two strings without using library functions.

In this approach, we implement functionality of strcmp() without using strcmp() function.

/* Compare two strings without using library functions, by using user defined function */

#include <stdio.h>
 
int string_comparison(char [], char []);
 
int main()
{
	char string1[100], string2[100];
 
	printf("\n Enter first string:- ");
	gets(string1);
   
	printf("\n Enter second string:- ");
	gets(string2);
 
	if (string_comparison(string1, string2) == 0)
		printf("\n Equal strings.\n");
	else
		printf("\n Unequal strings.\n");
 
	return 0;
}
 
int string_comparison(char a[], char b[])
{
	int i = 0;
 
	while (a[i] == b[i])
	{
		if (a[i] == '\0' || b[i] == '\0')
		break;
		i++;
	}
   
	if (a[i] == '\0' && b[i] == '\0')
		return 0;
	else
		return -1;
}

4. Compare two strings using macros in C:

Thi way actually combines macros and strcmp() to compare two strings.

/* Aim: Define a macro EQUALSTR which
compares two strings x and y and gives 1 if 
equal and 0 otherwise. Use this macro to 
accept two strings from the user and check if they are equal. */

#include<stdio.h>
#include<string.h>

#define EQUALSTR(x,y) strcmp(x,y)==0?1:0 

void main()
{
	char str1[100],str2[100];

	printf("\n Enter two strings:- ");
	scanf("%s%s",str1,str2);

	if(EQUALSTR(str1,str2))
	printf("\n Two strings are equal \n \n");
	else
	printf("\n Two strings are not equal \n \n");
}

Output

 Output of above code:- 
 Enter two strings:- Halo Halo
 Two strings are equal