Making Comparisons Using the C strcmp Function

In programming, the ability to manipulate and compare strings is a fundamental skill that has applications across various domains. Whether you're building a user authentication system, parsing text data, or developing algorithms that rely on string matching, understanding how to handle strings effectively is crucial.

For beginners embarking on their journey into C programming, mastering the `strcmp` function is essential to unlocking the power of string comparisons. This comprehensive guide will take you through the basics of C programming, laying a solid foundation before diving into the intricacies of the `strcmp` function.

Setting the Stage: C Programming Fundamentals

Before we delve into string comparisons, it's essential to have a firm grasp of the fundamental concepts in C programming. Let's begin with the building blocks:

Variables and Data Types

Variables are the backbone of any programming language, allowing you to store and manipulate data. In C, you must declare a variable's data type before using it. Here are some common data types:

int age = 25; // Integer

float height = 1.75; // Floating-point number

char grade = 'A'; // Character

Control Structures

Control structures are essential for controlling the flow of your program based on certain conditions. The `if` statement is a common control structure used for decision-making:

int age = 18;

if (age >= 18) {

    printf("You are an adult.\n");

} else {

    printf("You are a minor.\n");


The `for` loop is another essential control structure used for iterating over a block of code a specific number of times:

for (int i = 0; i < 5; i++) {

    printf("Iteration %d\n", i);



Functions are reusable blocks of code that perform specific tasks. In C, you must declare a function's return type and parameters before defining its body:

int add(int a, int b) { // Function declaration

    int result = a + b;

    return result;


int main() {

    int sum = add(3, 4); // Calling the function

    printf("Sum: %d\n", sum);

    return 0;


Arrays and Strings

Arrays are powerful data structures that allow you to store and manipulate collections of values of the same data type. In C, strings are represented as character arrays, with a null terminator (`\0`) marking the end of the string:

char name[] = "Alice"; // String declaration and initialization

int length = strlen(name); // Getting the length of the string (without null terminator)

printf("Name: %s\n", name); // Printing the string

Now that you have a solid foundation in C programming, let's dive into the world of string comparisons and explore the `strcmp` function.

Introducing `strcmp`: The String Comparison Function

The `strcmp` function is a powerful tool in the C standard library that allows you to compare two strings. It stands for "string compare" and is declared in the `string.h` header file. The function takes two strings as arguments and returns an integer value indicating the result of the comparison.

Here's the syntax for using `strcmp`:

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

  • `str1` and `str2` are the two strings being compared.
  • The function returns an integer value based on the comparison:
    • `0` if the strings are equal
    • A negative value if `str1` is lexicographically less than `str2`
    • A positive value if `str1` is lexicographically greater than `str2`

Lexicographical order is determined by the ASCII values of the characters in the strings. For example, "apple" comes before "banana" because the ASCII value of 'a' (97) is less than the ASCII value of 'b' (98).

Putting `strcmp` into Practice

Let's explore some practical examples to solidify your understanding of the `strcmp` function:

Comparing Two Strings

#include <stdio.h>

#include <string.h>

int main() {

    char str1[] = "hello";

    char str2[] = "world";

    char str3[] = "hello";

    int result1 = strcmp(str1, str2); // Compare "hello" and "world"

    int result2 = strcmp(str1, str3); // Compare "hello" and "hello"

    printf("Comparing 'hello' and 'world': %d\n", result1); // Output: -1 (negative value)

    printf("Comparing 'hello' and 'hello': %d\n", result2); // Output: 0 (equal)

    return 0;


In this example, we compare the strings "hello" and "world", as well as two instances of "hello". The output shows that `strcmp` returns a negative value when the first string is lexicographically less than the second, and 0 when the strings are equal.

Implementing a Simple String Comparison Function

#include <stdio.h>

#include <string.h>

int stringCompare(char *str1, char *str2) {

    int result = strcmp(str1, str2);

    if (result == 0) {

        printf("The strings are equal.\n");

    } else if (result < 0) {

        printf("%s is lexicographically less than %s.\n", str1, str2);

    } else {

        printf("%s is lexicographically greater than %s.\n", str1, str2);


    return result;


int main() {

    char input1[100];

    char input2[100];

    printf("Enter the first string: ");

    fgets(input1, sizeof(input1), stdin);

    input1[strcspn(input1, "\n")] = '\0'; // Remove newline character

    printf("Enter the second string: ");

    fgets(input2, sizeof(input2), stdin);

    input2[strcspn(input2, "\n")] = '\0'; // Remove newline character

    stringCompare(input1, input2);

    return 0;


In this example, we create a `stringCompare` function that takes two strings as input, compares them using `strcmp`, and prints the result. The program prompts the user to enter two strings and then calls the `stringCompare` function with the input strings.

This example demonstrates how `strcmp` can be used in a practical scenario, such as implementing a simple string comparison utility.

The Importance of String Comparisons in Programming

String comparisons are an essential part of programming, with applications in various domains. Here are some scenarios where string comparisons play a crucial role:

  1. User Authentication: In user authentication systems, string comparisons are used to verify user credentials (e.g., usernames and passwords) against stored values.
  2. Data Parsing and Validation: When working with text-based data formats (e.g., CSV, XML, JSON), string comparisons are often employed to validate and parse the data correctly.
  3. Algorithm Implementation: Many algorithms, such as searching, sorting, and pattern matching, rely on string comparisons to perform their operations efficiently.
  4. Database Operations**: In database systems, string comparisons are used to query, filter, and manipulate textual data stored in tables.
  5. Natural Language Processing: In natural language processing applications, string comparisons are utilized for tasks like spell checking, text similarity analysis, and information retrieval.

By mastering the `strcmp` function and understanding the importance of string comparisons, you'll be well-equipped to tackle various programming challenges and develop robust, efficient solutions.

Continuing Your C Programming Journey

While the `strcmp` function is a valuable tool in your programming arsenal, it's just the tip of the iceberg regarding C programming. There are countless other functions and concepts to explore, ranging from advanced string manipulation to file handling, data structures, and more.

Here are some additional topics you might consider delving into as you continue your journey in C programming:

  1. Pointers and Memory Management: Pointers are a fundamental concept in C programming, allowing you to work with memory addresses and perform dynamic memory allocation and deallocation.
  2. File I/O Operations: Learn how to read from and write to files, enabling you to persist and retrieve data efficiently.
  3. Data Structures and Algorithms: Explore various data structures (e.g., linked lists, trees, stacks, queues) and algorithms (e.g., sorting, searching, graph traversal) to solve complex problems efficiently.
  4. Preprocessor Directives: Understand the role of preprocessor directives in C programming, such as macros, conditional compilation, and file inclusion.
  5. Libraries and APIs: Discover the vast ecosystem of C libraries and APIs that extend the language's functionality, enabling you to leverage existing code and tools for your projects.

Remember, programming is a journey of continuous learning and practice. Embrace challenges, experiment with different approaches, and don't hesitate to seek guidance from experienced programmers, online resources, and the vibrant C programming community.

By mastering the `strcmp` function and building a strong foundation in C programming, you've taken a significant step toward becoming a proficient programmer capable of tackling complex problems and creating powerful applications.

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