Add password strength checker in C

password_strength_checker/README.md

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+# Password Strength Checker
+
+A simple C program that evaluates the strength of a password based on various criteria.
+
+## Description
+
+This program analyzes a password and determines its strength based on the following factors:
+- Presence of uppercase letters
+- Presence of lowercase letters
+- Presence of digits
+- Presence of special characters
+- Minimum length of 8 characters
+
+## Features
+
+- Real-time password strength evaluation
+- Three strength levels: Weak, Medium, and Strong
+- Simple command-line interface
+- Character type detection (uppercase, lowercase, digits, special characters)
+
+## Compilation
+
+To compile the program, use any C compiler such as GCC:
+
+```bash
+gcc password_checker.c -o password_checker
+```
+
+## Usage
+
+Run the compiled program:
+
+```bash
+./password_checker
+```
+
+Enter your password when prompted. The program will analyze it and display the strength level.
+
+### Example
+
+```
+Enter your password: MyP@ss123
+
+Password Strength: Strong
+```
+
+## Strength Criteria
+
+The program calculates strength based on a scoring system (0-5 points):
+
+- **Weak** (0-2 points): Password lacks multiple character types or is too short
+- **Medium** (3-4 points): Password has good variety but may be missing some criteria
+- **Strong** (5 points): Password meets all criteria including length and character variety
+
+### Scoring Breakdown
+- 1 point: Contains uppercase letters
+- 1 point: Contains lowercase letters
+- 1 point: Contains digits
+- 1 point: Contains special characters
+- 1 point: Length is 8 or more characters
+
+## Limitations
+
+- The program uses `scanf("%s", password)` which stops at whitespace, so passwords containing spaces cannot be fully tested
+- Maximum password length is limited to 99 characters
+- No buffer overflow protection beyond the array size
+- Doesn't check against common password lists or patterns
+
+## Security Note
+
+This is a basic educational tool for demonstrating password strength concepts. For production applications, use established password validation libraries and follow current security best practices.
+
+## Requirements
+
+- C compiler (GCC, Clang, or similar)
+- Standard C library with `stdio.h`, `string.h`, and `ctype.h`
+
+## License
+
+Free to use and modify for educational purposes.

password_strength_checker/password-strength-checker.c

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+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+#define MAX_PASSWORD_LENGTH 100
+#define MIN_PASSWORD_LENGTH 8
+
+int main() {
+    char password[MAX_PASSWORD_LENGTH];
+    size_t length = 0;
+    int upper = 0;
+    int lower = 0;
+    int digit = 0;
+    int special = 0;
+
+    printf("Enter your password: ");
+    scanf("%99s", password); // Safe input, avoids buffer overflow
+
+    length = strlen(password);
+
+    for (size_t i = 0; password[i] != '\0'; i++) {
+        if (isupper(password[i])) {
+            upper = 1;
+        } else if (islower(password[i])) {
+            lower = 1;
+        } else if (isdigit(password[i])) {
+            digit = 1;
+        } else {
+            special = 1;
+        }
+    }
+
+    int strength = upper + lower + digit + special + (length >= MIN_PASSWORD_LENGTH ? 1 : 0);
+
+    printf("\nPassword Strength: ");
+    if (strength <= 2) {
+        printf("Weak\n");
+    } else if (strength == 3 || strength == 4) {
+        printf("Medium\n");
+    } else {
+        printf("Strong\n");
+    }
+
+    return 0;
+}