C Program: User input validation with While Loop for minimum 8-Character username

C While Loop: Exercise-7 with Solution

Write a C program that prompts the user to input a username. Use a while loop to keep asking for a username until a valid one is entered (e.g., at least 8 characters long).

Sample Solution:

C Code:

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

int main() {
    char username[20];  // Array to store the user input for the username

    // Start a while loop to keep asking for a valid username
    while (1) {
        // Prompt the user to input a username
        printf("Input a username (at least 8 characters): ");
        scanf("%s", username);  // Read the user input and store it in the array

        // Check if the entered username is at least 8 characters long
        if (strlen(username) >= 8) {
            break;  // Exit the loop if the username is valid
        } else {
            // Print an error message if the username is too short
            printf("Error: Username must be at least 8 characters long.\n");
        }

        // Clear the input buffer to handle any remaining characters
        while (getchar() != '\n');
    }

    // Print a message indicating a valid username was entered
    printf("Valid username entered: %s\n", username);

    return 0;  // Indicate successful program execution
}

Sample Output:

Input a username (at least 8 characters): Sdk34%k
Error: Username must be at least 8 characters long.
Input a username (at least 8 characters): Akdsui234#$
Valid username entered: Akdsui234#$

Explanation:

Here are key parts of the above code step by step:

• #include <stdio.h>: Include the standard input-output library for functions like "printf()" and "scanf()".
• #include <string.h>: Include the string manipulation library for functions like strlen.
• int main() {: Start the main function.
• char username[20];: Declare a character array 'username' to store the user input for the username.
• while (1) {: Start an infinite while loop.
• printf("Enter a username (at least 8 characters): ");: Prompt the user to enter a username.
• scanf("%s", username);: Read the user input and store it in the 'username' array.
• if (strlen(username) >= 8) {: Check if the entered username is at least 8 characters long using 'strlen'.
• break;: Exit the loop if the username is valid.
• } else { printf("Error: Username must be at least 8 characters long.\n"); }: Print an error message if the username is too short.
• while (getchar() != '\n');: Clear the input buffer to handle any remaining characters.
• }: Close the while loop.
• printf("Valid username entered: %s\n", username);: Print a message indicating a valid username was entered.
• return 0;: Indicate successful program execution.
• }: Close the main function.

Flowchart:

C Programming Code Editor:

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