How to Compare Two Strings Without Using Built-In Functions

When developing software, sometimes you need to compare two strings without relying on built-in string functions. This can be done for various reasons, such as understanding underlying mechanisms, learning new programming techniques, or ensuring portability. In this article, we explore how to manually compare two strings in C and Python, without using string library functions.

String Comparison in C

In C, you can manually compare two strings by iterating over each character of both strings and comparing them one by one. This approach avoids using built-in functions like strcmp, which are already optimized and widely used.

int my_strcmp(const char* s1, const char* s2) {    char* ptr1  s1;    char* ptr2  s2;    // compare each character until either string hits NUL terminator.    while (*ptr1 ! 0  *ptr2 ! 0) {        // find lexically higher string.        if (*ptr1  *ptr2) {            // s1  s2            return 1;        }        else if (*ptr1  *ptr2) {            // s1  s2            return -1;        }        // increment both pointers.        ptr1  ;        ptr2  ;    }    // reached end of at least one string.    if (*ptr1  0  *ptr2  0) {        // s1  s2        return 0;    }    else if (*ptr1  0) {        // s1  s2        return -1;    }    else if (*ptr2  0) {        // s1  s2        return 1;    }}

This implementation uses pointer arithmetic to traverse the char arrays. It returns an integer indicating whether s1 is lexically less than, equal to, or greater than s2. The function is tested in the main function to ensure its correctness.

String Comparison in Python

You can also implement a similar function in Python without using built-in string functions. Here's a simple implementation:

def comparestrings(s1, s2):    # Compare lengths first    if len(s1) ! len(s2):        return False    # Compare character by character    for i in range(len(s1)):        if s1[i] ! s2[i]:            return False    return True

The function comparestrings first checks if the lengths of the two strings are the same. If not, it returns False. Then it iterates over each character using a loop. If any character does not match, it returns False. If all characters match, it returns True.

Conclusion

While built-in string functions like strcmp are efficient and widely used, understanding how to compare strings manually can be a valuable skill. It enhances your knowledge of programming and ensures that your code is robust and can operate in environments where built-in functions may not be available.

Key Takeaways

Comparing strings manually can be useful for learning and ensuring code portability. Use pointer arithmetic in C to traverse char arrays. Implement a for loop in Python to iterate over each character.