C Program to Compare Two Strings

Understanding Strings in C

Before we begin comparing strings, let’s have a quick overview of what strings are in the context of C programming. In C, a string is an array of characters terminated by a null character (‘\0’). Each character in the string is represented by its ASCII value, enabling us to perform various operations on strings.

Now that we have a basic understanding of strings, let’s move on to exploring the different methods of comparing strings in C.

The strcmp() Function

C provides us with a built-in function called strcmp() that is specifically designed for comparing strings. This function takes two string arguments and returns an integer value based on the comparison result. Let’s take a closer look at the syntax of strcmp():

int strcmp(const char *str1, const char *str2)

The strcmp() function compares the string str1 with the string str2. Here’s what the return value of strcmp() signifies:

• If the return value is less than 0, it means str1 is lexicographically less than str2.

• If the return value is greater than 0, it means str1 is lexicographically greater than str2.

• If the return value is 0, it means str1 is equal to str2.

Let’s look at an example to make things clearer:

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

int main() {
    char str1[20] = "Hello";
    char str2[20] = "World";

    int result = strcmp(str1, str2);

    if (result < 0) {
        printf("str1 is less than str2\n");
    } else if (result > 0) {
        printf("str1 is greater than str2\n");
    } else {
        printf("str1 is equal to str2\n");
    }

    return 0;
}

In the above example, we have two strings str1 and str2. We use strcmp() to compare them and store the result in the result variable. Depending on the value of result, we print the appropriate message. When we run this program, it will output str1 is less than str2 because “Hello” comes before “World” lexicographically according to ASCII values.

The strncmp() Function

Besides strcmp(), C also provides us with another function called strncmp() that allows us to compare a specified number of characters of two strings. The syntax for strncmp() is as follows:

int strncmp(const char *str1, const char *str2, size_t num)

The strncmp() function compares at most num characters of string str1 with string str2. The return value follows the same convention as strcmp().

Here’s an example that demonstrates the usage of strncmp():

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

int main() {
    char str1[20] = "Hello World";
    char str2[20] = "Hello World!";
    
    int result = strncmp(str1, str2, 5);

    if (result < 0) {
        printf("str1 is less than str2\n");
    } else if (result > 0) {
        printf("str1 is greater than str2\n");
    } else {
        printf("str1 is equal to str2\n");
    }

    return 0;
}

In the above example, we compare the first 5 characters of the two strings, “Hello” and “Hello”. As a result, the program outputs str1 is equal to str2 since the first 5 characters are the same in both strings.

Alternative Approaches to String Comparison

While strcmp() and strncmp() are the most common methods of comparing strings in C, there are alternative approaches that can be useful in certain situations.

Using a Loop

One approach is to manually compare the characters of the strings using a loop. We can iterate through each character of the strings and compare them one by one until we find a mismatch or reach the end of either string. Here’s an example:

#include <stdio.h>

int strcmp_loop(const char *str1, const char *str2) {
    int i = 0;

    while (str1[i] != '\0' || str2[i] != '\0') {
        if (str1[i] < str2[i]) {
            return -1;
        } else if (str1[i] > str2[i]) {
            return 1;
        }

        i++;
    }

    return 0;
}

int main() {
    char str1[20] = "Hello";
    char str2[20] = "World";

    int result = strcmp_loop(str1, str2);

    if (result < 0) {
        printf("str1 is less than str2\n");
    } else if (result > 0) {
        printf("str1 is greater than str2\n");
    } else {
        printf("str1 is equal to str2\n");
    }

    return 0;
}

In the above example, we define a custom function strcmp_loop() that compares the strings str1 and str2 character by character. The function uses a loop to iterate through the characters and returns a value based on the comparison result.

Converting to ASCII Values

Another alternative approach is to compare the ASCII values of the characters directly. This method works because each character in C is represented by its ASCII value. Here’s an example:

#include <stdio.h>

int strcmp_ascii(const char *str1, const char *str2) {
    int i = 0;

    while (str1[i] != '\0' || str2[i] != '\0') {
        if (str1[i] - str2[i] < 0) {
            return -1;
        } else if (str1[i] - str2[i] > 0) {
            return 1;
        }

        i++;
    }

    return 0;
}

int main() {
    char str1[20] = "Hello";
    char str2[20] = "World";

    int result = strcmp_ascii(str1, str2);

    if (result < 0) {
        printf("str1 is less than str2\n");
    } else if (result > 0) {
        printf("str1 is greater than str2\n");
    } else {
        printf("str1 is equal to str2\n");
    }

    return 0;
}

In this example, we define the strcmp_ascii() function that compares the strings str1 and str2 by subtracting their ASCII values. The function uses a loop similar to the previous approach and provides the same comparison result.

Conclusion

In this blog post, we’ve explored how to compare two strings in C. We’ve learned about the strcmp() and strncmp() functions that are specifically designed for string comparison. We’ve also discussed alternative approaches using loops and direct comparison of ASCII values. All these methods provide us with the means to compare strings and determine their relative order.

Whether you’re a beginner just starting your programming journey or an experienced developer looking to refresh your knowledge, understanding string comparison in C is a fundamental skill. By mastering these techniques, you’ll be able to write more complex programs that involve manipulating and analyzing text.

As you continue your programming journey, don’t forget to practice writing C programs and experiment with different string comparison techniques. By doing so, you’ll gain a deeper understanding of strings and sharpen your programming skills.

So keep coding, keep exploring, and keep pushing the boundaries of what you can create with C!