Random password generator in C

In this article, we will delve into an interesting and practical problem related to string manipulation in C programming. We are going to build a "Random Password Generator" in C. This problem not only enhances your understanding of string manipulation but also your knowledge of the C Standard Library.

Problem Statement

The task is to build a program that generates a random password of a specified length. The password should include uppercase and lowercase alphabets, digits, and special characters.

C Solution Approach

To solve this problem, we'll leverage the power of the C Standard Library. We'll use the rand() function to generate random numbers within a specified range. We'll create a string of all possible characters that our password can contain, and then for each character in our password, we'll randomly select a character from this string.


Here's the C code that implements a random password generator −

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void generatePassword(int len) {
   char possibleChars[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890!@#$%^&*()";
   char password[len+1];
   srand(time(0)); // seed for random number generation
   for(int i = 0; i < len; i++) {
      int randomIndex = rand() % (sizeof(possibleChars) - 1);
      password[i] = possibleChars[randomIndex];
   password[len] = '\0'; // null terminate the string
   printf("The randomly generated password is: %s\n", password);

int main() {
   int len = 10; // desired length of password
   return 0;


The randomly generated password is: )^a3cJciyk

Explanation with a Test Case

Let's say we want to generate a password of length 10.

When we pass this length to the generate Password function, it generates a random password with 10 characters.

The function constructs a string of all possible characters that the password can contain. Then it uses the rand() function to generate a random index, which is used to pick a character from the string of possible characters. It repeats this process for the specified length of the password.

Please note that each time you run this program, it will generate a different password due to the random nature of our algorithm.


This problem presents an interesting use case of random number generation and string manipulation in C. It's a fantastic problem to understand and practice how to use the C Standard Library effectively.

Updated on: 18-May-2023


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