Write A Program To Find The Length Of The String Without Using Strlen () Function In C

In C programming, strings are arrays of characters terminated by a null character (\0). Understanding how to manipulate these strings manually is crucial for deeper comprehension of the language. In this article, you will learn how to determine the length of a string without using the standard library function strlen(), focusing on fundamental loop-based approaches.

Problem Statement

While the strlen() function from provides a convenient way to find the length of a string, there are scenarios where understanding its underlying logic or implementing a custom version is beneficial. This could be for educational purposes, working in environments with restricted standard library access, or simply for debugging and optimizing string operations by knowing how they fundamentally work. The core problem is to count the number of characters in a given string until the null terminator is encountered.

Example

Consider the string "programming". The desired output for its length would be 11. Similarly, for the string "C", the length is 1.

Background & Knowledge Prerequisites

To effectively follow this guide, readers should have a basic understanding of:

• C Fundamentals: Basic syntax, variable declaration, and data types.
• Character Arrays: How strings are represented in C as arrays of char.
• Null Terminator (\0): The special character that marks the end of a C string.
• Loops: Familiarity with for and while loops.
• Pointers (optional but helpful): Understanding how character pointers can traverse strings.

Use Cases or Case Studies

Manually finding string length can be valuable in several contexts:

• Educational Purposes: Solidifies understanding of how strings are stored and processed in C.
• Custom String Libraries: When building your own string manipulation functions, strlen() might be one of the first functions you implement.
• Embedded Systems: In resource-constrained environments, strlen() might not always be available or its implementation might be optimized differently, necessitating a custom approach.
• Algorithm Development: As a building block for more complex string processing algorithms, such as string concatenation or substring extraction, where you need precise control over string boundaries.
• Debugging: Understanding the manual process can help in debugging issues related to string termination or buffer overflows.

Solution Approaches

We will explore two common loop-based approaches to find the string length without strlen().

Approach 1: Using a for loop with array indexing

This approach iterates through the string using a for loop and an index, incrementing a counter until the null terminator is found.

// String Length with For Loop
#include <stdio.h>

int main() {
    char str[] = "Hello World"; // The string to measure
    int length = 0;              // Variable to store the length
    
    // Step 1: Iterate through the string using a for loop
    // The loop continues as long as the current character is not the null terminator '\\0'
    for (int i = 0; str[i] != '\\0'; i++) {
        // Step 2: Increment the length counter for each character found
        length++;
    }
    
    // Step 3: Print the calculated length
    printf("The string is: \\"%s\\"\\n", str);
    printf("Length of the string (for loop): %d\\n", length);
    
    return 0;
}

Run

Sample Output:

The string is: "Hello World"
Length of the string (for loop): 11

Stepwise Explanation:

1. Initialize a character array str with the desired string and an integer variable length to 0.
2. Start a for loop with an index i initialized to 0.
3. The loop continues as long as the character at str[i] is not the null terminator (\0).
4. In each iteration, the length variable is incremented, effectively counting each character before the null terminator.
5. After the loop finishes, length holds the total count of characters, which is then printed.

Approach 2: Using a while loop with a pointer

This method uses a while loop and a character pointer to traverse the string, incrementing a counter until the pointer reaches the null terminator.

// String Length with While Loop and Pointer
#include <stdio.h>

int main() {
    char str[] = "C Programming"; // The string to measure
    char *ptr = str;             // Pointer to the beginning of the string
    int length = 0;              // Variable to store the length
    
    // Step 1: Iterate through the string using a while loop and pointer
    // The loop continues as long as the character pointed to is not the null terminator '\\0'
    while (*ptr != '\\0') {
        // Step 2: Increment the length counter
        length++;
        // Step 3: Move the pointer to the next character
        ptr++;
    }
    
    // Step 4: Print the calculated length
    printf("The string is: \\"%s\\"\\n", str);
    printf("Length of the string (while loop with pointer): %d\\n", length);
    
    return 0;
}

Run

Sample Output:

The string is: "C Programming"
Length of the string (while loop with pointer): 13

Stepwise Explanation:

1. Initialize a character array str and an integer length to 0.
2. Declare a character pointer ptr and initialize it to point to the beginning of str.
3. Start a while loop. The loop condition checks if the character *pointed to* by ptr is not the null terminator (\0).
4. Inside the loop, length is incremented.
5. The pointer ptr is then incremented (ptr++), moving it to point to the next character in the string.
6. The loop terminates when ptr points to the null terminator.
7. Finally, length contains the accurate count of characters.

Conclusion

Determining the length of a string without strlen() is a fundamental exercise in C programming that deepens understanding of character arrays and null termination. Both for and while loop approaches effectively achieve this by iterating through the string until the null terminator is encountered, incrementing a counter along the way. These manual methods are essential for building foundational knowledge and can be applied in various programming contexts.

Summary

• String Representation: C strings are character arrays terminated by a null character (\0).
• Manual Length Calculation: Involves iterating through the string, character by character, until the null terminator is reached.
• for Loop Approach: Uses an index to access each character, incrementing a counter on each non-null character.
• while Loop with Pointer Approach: Uses a character pointer to traverse the string, incrementing both the pointer and a counter until the null terminator is encountered.
• Importance: Critical for understanding string mechanics, custom library development, and educational purposes.