FAQs in C: Find the Length of a String

In this article, we provide a comprehensive guide to finding the length of a string in C. You’ll find a clear algorithm, the complete C program, and a step-by-step explanation of each part of the process. This guide is perfect for beginners and intermediate programmers looking to understand string manipulation in C.

Method 1: Using fgets from the standard input-output library

Algorithm to Find the Length of a String

Step 1: Start
Step 2: Input: Read the string from the user.
Step 3: Initialize Counter: Set the counter to 0.

Step 4: Iterate Through the String:
        (i) Loop through each character of the string until the null 
            character ('\0') is encountered.
        
        (ii) Increment the counter for each character.

Step 5: Output: Display the counter as the length of the string.
Step 6: End

C Program to Find the Length of a String

#include <stdio.h>

int main() {
    char str[100];
    int length = 0;

    // Step 2: Input the string
    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);

    // Step 4: Iterate through the string to calculate its length
    while (str[length] != '\0') {
        length++;
    }

    // If the last character is a newline (due to fgets), decrement the length
    if (str[length - 1] == '\n') {
        length--;
    }

    // Step 5: Output the length of the string
    printf("Length of the string is: %d\n", length);

    // Step 6: End
    return 0;
}

Explanation of Each Step

Include Header:

#include <stdio.h>

• This line includes the standard input-output library for using functions like printf and fgets.

Input the String:

char str[100];
int length = 0;

printf("Enter a string: ");
fgets(str, sizeof(str), stdin);

• These lines declare a character array to store the string and an integer to count the length.
• The fgets function reads a line of text from the standard input and stores it in str.

Initialize Counter:

int length = 0;

• This line initializes the counter length to 0.

Iterate through the string:

while (str[length] != '\0') {
    length++;
}

if (str[length - 1] == '\n') {
    length--;
}

• The while loop iterates through each character in the string until it encounters the null character (‘\0’), incrementing the counter length for each character.

• If the last character is a newline (because fgets includes the newline character), the length is decremented by 1 to exclude it.

Output of the Length of the String:

printf("Length of the string is: %d\n", length);

• This line prints the calculated length of the string.

End:

return 0;

• This line indicates the successful completion of the program.

Summary

This program efficiently calculates and prints the length of a string input by the user. It uses basic string handling techniques in C, demonstrating how to iterate through a string and count its characters.

Method 2: Using the ‘strlen’ function

Using the strlen function from the C standard library, we can simplify the program even further. The strlen function calculates the length of a string excluding the null terminator (‘\0’).

Simplified Algorithm to Find the Length of a String Using strlen

Step 1: Start
Step 2: Input: Read the string from the user.
Step 3: Calculate Length: Use the strlen function to determine            
        the length of the string.

Step 4: Output: Display the length of the string.
Step 5: End

C Program to Find the Length of a String Using strlen

#include <stdio.h>
#include <string.h> // Include the string.h library for strlen

int main() {
    char str[100];

    // Step 2: Input the string
    printf("Enter a string: ");
    scanf("%s", str);

    // Step 3: Calculate the length using strlen
    int length = strlen(str);

    // Step 4: Output the length of the string
    printf("Length of the string is: %d\n", length);

    // Step 5: End
    return 0;
}

Explanation of Each Step

Include Header Files:

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

These lines include the standard input-output library for using functions like printf and scanf, and the string library for using strlen.

Input the String:

char str[100];

printf("Enter a string: ");
scanf("%s", str);

• These lines declare a character array to store the string and use scanf to read a word (a sequence of characters without spaces) from the standard input and store it in str.

Calculate Length Using strlen:

int length = strlen(str);

• The strlen function is called to calculate the length of the string (excluding the null terminator).

Output the Length of the String:

printf("Length of the string is: %d\n", length);

• This line prints the calculated length of the string.

End:

return 0;

Summary

This simplified program uses the strlen function to efficiently calculate and print the length of a string input by the user, using scanf to read the string. Note that scanf stops reading input at the first whitespace character, so it is suitable for reading a single word. If you need to handle spaces in the input, you would need a different approach, such as using gets or fgets with manual handling of the newline character.