Remove Non-Alphabetic Characters from Strings in C

Getting Started: Understanding the Basics

Before diving into the program, make sure you have a solid grasp of the following C programming concepts:

• Arrays
• Strings
• For loops
• While and do…while loops

If you’re new to these topics, take a moment to review them before proceeding.

The Program: Removing Non-Alphabetic Characters

#include <stdio.h>
#include <ctype.h>

int main() {
    char line[100];
    char result[100] = "";
    int i, j = 0;

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

    for (i = 0; line[i]; i++) {
        if (isalpha(line[i])) {
            result[j++] = line[i];
        }
    }

    result[j] = '\0';
    printf("Output: %s\n", result);

    return 0;
}

The Logic Behind the Program

The program works as follows:

1. We initialize an empty string, result, to store the filtered characters.
2. The for loop iterates over each character in the input string, checking if it’s an alphabet using the isalpha() function.
3. If the character is an alphabet, we append it to the result string.
4. Once the loop completes, we’re left with a string containing only alphabetic characters.

Sample Output

Try running the program with the input "Hello, World! 123" and see the output:

Output: "HelloWorld"

This program demonstrates the power of C programming in removing unwanted characters from strings, leaving behind only the alphabets.