C Program: Password authentication with Do-While Loop

Last update on July 30 2025 12:56:15 (UTC/GMT +8 hours)

8. Password Validation

Write a C program that prompts the user to enter a password. Use a do-while loop to keep asking for the password until the correct one is entered.

Sample Solution:

C Code:

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

int main() {
    char correctPassword[] = "pass$123";  // Set the correct password
    char enteredPassword[20];  // Variable to store the user-entered password

    // Use a do-while loop to repeatedly ask for the password
    do {
        // Prompt the user to enter the password
        printf("Input the password: ");
        scanf("%s", enteredPassword);

        // Check if the entered password is correct
        if (strcmp(enteredPassword, correctPassword) == 0) {
            printf("Correct password! Access granted.\n");
            break;  // Exit the loop if the password is correct
        } else {
            printf("Incorrect password. Try again.\n");
        }

    } while (1);  // Continue the loop indefinitely until the correct password is entered

    return 0;  // Indicate successful program execution
}

Sample Output:

Input the password: pass123$
Incorrect password. Try again.
Input the password: pass123#
Incorrect password. Try again.
Input the password: 123pass$
Incorrect password. Try again.
Input the password: pass123$
Incorrect password. Try again.
Input the password: pass$123
Correct password! Access granted.

Explanation:

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

char correctPassword[] = "pass$123";: Sets the correct password as a string.
char enteredPassword[20];: Declares an array to store the user-entered password.
do { ... } while (1);: Creates a do-while loop that continues indefinitely.
printf("Enter the password: ");: Prompts the user to enter the password.
scanf("%s", enteredPassword);: Reads the user's input into the 'enteredPassword' array.
if (strcmp(enteredPassword, correctPassword) == 0) { ... }: Compares the entered password with the correct password using strcmp.
printf("Correct password! Access granted.\n");: Displays a success message if the password is correct.
break;: Exits the loop if the correct password is entered.
else { printf("Incorrect password. Try again.\n"); }: Displays an error message if the password is incorrect.
} while (1);: Continues the loop until the correct password is entered.
return 0;: Indicates successful program execution.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program that prompts the user for a password and allows only three incorrect attempts before exiting.
Write a C program to accept a password input until it meets specific security requirements (e.g., uppercase, digit, special character).
Write a C program to prompt the user for a password but display only '*' for each character entered.
Write a C program to verify a password by comparing it with a stored password and allowing retry if incorrect.

Go to:

PREV : Average of User Input Numbers.
NEXT : Sum of Prime Numbers.

C Programming Code Editor:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.