String comparison

Introduction

We compare strings to check if two words or sentences are the same or to find which one comes first in order.

Checking if a username matches a stored name.

Sorting a list of words alphabetically.

Finding if a password entered matches the saved password.

Comparing two text inputs to see if they are equal.

Syntax

C

#include <string.h>

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

strcmp returns 0 if the strings are exactly the same.

If the first string is 'less' than the second, strcmp returns a negative number; if 'greater', a positive number.

Examples

This compares two identical strings and result will be 0.

C

#include <string.h>

int result = strcmp("apple", "apple");

Since "apple" comes before "banana", result will be negative.

C

int result = strcmp("apple", "banana");

Since "banana" comes after "apple", result will be positive.

C

int result = strcmp("banana", "apple");

Sample Program

This program compares two pairs of strings and prints the results and their order.

C

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

int main() {
    char str1[] = "hello";
    char str2[] = "hello";
    char str3[] = "world";

    int res1 = strcmp(str1, str2);
    int res2 = strcmp(str1, str3);

    printf("Compare str1 and str2: %d\n", res1);
    printf("Compare str1 and str3: %d\n", res2);

    if (res1 == 0) {
        printf("str1 and str2 are the same.\n");
    } else {
        printf("str1 and str2 are different.\n");
    }

    if (res2 < 0) {
        printf("str1 comes before str3.\n");
    } else if (res2 > 0) {
        printf("str1 comes after str3.\n");
    } else {
        printf("str1 and str3 are the same.\n");
    }

    return 0;
}

Important Notes

Always include to use strcmp.

strcmp compares strings letter by letter using ASCII values.

Do not use == to compare strings in C; it compares addresses, not content.

Summary

Use strcmp to compare two strings in C.

strcmp returns 0 if strings are equal, negative if first is less, positive if first is greater.

Always include and do not use == for string content comparison.