C Program to Compare Two Strings Using Pointers

In C, strings are arrays of characters terminated by a null character ('\0') and pointers can be used to traverse these arrays and compare the characters in two strings. In this article, we will learn how to compare two strings using pointers in C.

For Example,

Input:
char str1[] = "Hello";
char str2[] = "World";

Output:
Hello and World are not Equal

Comparing Two Strings Using Pointers in C

We can compare two strings using pointers by going through each character one by one and comparing whether it is equal or not till we reach the end of either string. The below approach defines how to do it.

Approach

1. Create a function that takes two character pointers as arguments that point to each string.
2. Iterate through the characters of both strings simultaneously using pointers and check if the current characters of both strings are equal, move to the next characters. If a pair of characters are not equal, return false.
3. If the end of both strings is reached without finding any unequal characters, return true, indicating that the strings are equal.
4. Based on the return value of the function, print whether the strings are equal or not.

C Program to Compare Two Strings Using Pointers

The below program demonstrates how we can compare the given strings using pointers in C.

C

// C Program to show how to compare two strings using
// pointers
#include <stdbool.h>
#include <stdio.h>

// Method to compare two strings using pointer
bool compare(char* str1, char* str2)
{
    // Iterating through the characters of both the strings
    while (*str1 == *str2) {
        if (*str1 == '\0' && *str2 == '\0')
            return true;
        str1++;
        str2++;
    }

    return false;
}

int main()
{
    // Declare and Initialize two strings
    char str1[] = "Hello";
    char str2[] = "World";

    // check if both strings are equal or not
    if (compare(str1, str2) == 1)
        printf("%s and %s are Equal", str1, str2);
    else
        printf("%s and %s are not Equal", str1, str2);

    return 0;
}

Output

Hello and World are not Equal

Time Complexity: O(N), here N is the length of the strings. 
Auxiliary Space: O(1)