Task: Password generator
C: #include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define DEFAULT_LENGTH 4
#define DEFAULT_COUNT 1

char* symbols[] = {"ABCDEFGHIJKLMNOPQRSTUVWXYZ", "abcdefghijklmnopqrstuvwxyz", "0123456789", "!\"#$%&'()*+,-./:;<=>?@[]^_{|}~"};
int length = DEFAULT_LENGTH;
int count = DEFAULT_COUNT;
unsigned seed;
char exSymbols = 0;

void GetPassword () {
    
    int lengths[4] = {1, 1, 1, 1};
    int count = 4;
    while (count < length) {
        lengths[rand()%4]++;
        count++;
    } 

    
    char password[length + 1];
    for (int i = 0; i < length; ) { 
        
        int str = rand()%4;
        if (!lengths[str])continue;   

        char c;
        switch (str) {
            case 2:
                c = symbols[str][rand()%10];
                while (exSymbols && (c == 'I' || c == 'l' || c == '1' || c == 'O' || c == '0' || c == '5' || c == 'S' || c == '2' || c == 'Z'))
                    c = symbols[str][rand()%10];
                password[i] = c;
            break;

            case 3:
                c = symbols[str][rand()%30];
                while (exSymbols && (c == 'I' || c == 'l' || c == '1' || c == 'O' || c == '0' || c == '5' || c == 'S' || c == '2' || c == 'Z'))
                    c = symbols[str][rand()%30];
                password[i] = c;
            break;

            default:
                c = symbols[str][rand()%26];
                while (exSymbols && (c == 'I' || c == 'l' || c == '1' || c == 'O' || c == '0' || c == '5' || c == 'S' || c == '2' || c == 'Z'))  
                    c = symbols[str][rand()%26];
                password[i] = c;
            break;
        }

        i++;
        lengths[str]--;
    }

    password [length] = '\0';
    printf ("%s\n", password);
}

int main (int argc, char* argv[]) {
    seed = (unsigned)time(NULL);

    
    for (int i = 1; i < argc; i++) {
        switch (argv[i][1]) {
            case 'l':
                if (sscanf (argv[i+1], "%d", &length) != 1) {
                    puts ("Unrecognized input. Syntax: -l [integer]");
                    return -1;
                }
                
                if (length < 4) {
                    puts ("Password length must be at least 4 characters.");
                    return -1;
                }
                i++;                
            break;

            case 'c':
                if (sscanf (argv[i+1], "%d", &count) != 1) {
                    puts ("Unrecognized input. Syntax: -c [integer]");
                    return -1;
                }

                if (count <= 0) {
                    puts ("Count must be at least 1.");
                    return -1;
                }
                i++;
            break;

            case 's':
                if (sscanf (argv[i+1], "%d", &seed) != 1) {
                    puts ("Unrecognized input. Syntax: -s [integer]");
                    return -1;
                }
                i++;
            break;

            case 'e':
                exSymbols = 1;
            break;

            default:
                help:
                printf ("Help:\nThis program generates a random password.\n"
                "Commands:"
                   "Set password length: -l [integer]\n"
                   "Set password count: -c [integer]\n"
                   "Set seed: -s [integer]\n"
                   "Exclude similiar characters: -e\n"
                   "Display help: -h");
                return 0;
            break;
        }    
    }

    srand (seed);

    for (int i = 0; i < count; i++)
        GetPassword();
    
    return 0;
}

C#: using System;
using System.Linq;

class Program
{
    const string Lower = "abcdefghijklmnopqrstuvwxyz";
    const string Upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    const string Digits = "0123456789";
    const string Symbols = "!\"#$%&'()*+,-./:;<=>?@[]^_{|}~";
    static readonly string[] Full = {Lower, Upper, Digits, Symbols, Lower + Upper + Digits + Symbols};

    const string Similar = "Il1O05S2Z";
    static readonly string[] Excluded = Full.Select(x => new string(x.Except(Similar).ToArray())).ToArray();

    static Random _rng = new Random();
    static string[] _symbolSet = Full;

    static void Main(string[] args)
    {
        int length = 12, count = 1;
        try
        {
            foreach (var x in args.Select(arg => arg.Split(':')))
            {
                switch (x[0])
                {
                    case "-l": length = int.Parse(x[1]); break;
                    case "-c": count = int.Parse(x[1]); break;
                    case "-s": _rng = new Random(x[1].GetHashCode()); break;
                    case "-x": _symbolSet = bool.Parse(x[1]) ? Excluded : Full; break;
                    default: throw new FormatException("Could not parse arguments");
                }
            }
        }
        catch { ShowUsage(); return; }
        try
        {
            for (int i = 0; i < count; i++)
                Console.WriteLine(GeneratePass(length));
        }
        catch (Exception ex) { Console.WriteLine("Error: " + ex.Message); }
    }

    static void ShowUsage()
    {
        Console.WriteLine("Usage: PASSGEN [-l:length] [-c:count] [-s:seed] [-x:(true|false)]");
        Console.WriteLine("\t-l: the length of the generated passwords");
        Console.WriteLine("\t-c: the number of passwords to generate");
        Console.WriteLine("\t-s: seed for the random number generator");
        Console.WriteLine("\t-x: exclude similar characters: " + Similar);
        Console.WriteLine("Example: PASSGEN -l:10 -c:5 -s:\"Sample Seed\" -x:true");
    }

    static string GeneratePass(int length)
    {
        var minLength = _symbolSet.Length - 1;
        if(length < minLength)
            throw new Exception("password length must be " + minLength + " or greater");

        int[] usesRemaining = Enumerable.Repeat(1, _symbolSet.Length).ToArray();
        usesRemaining[minLength] = length - minLength;
        var password = new char[length];
        for (int ii = 0; ii < length; ii++)
        {
            int set = _rng.Next(0, _symbolSet.Length);
            if (usesRemaining[set] > 0)
            {
                usesRemaining[set]--;
                password[ii] = _symbolSet[set][_rng.Next(0, _symbolSet[set].Length)];
            }
            else ii--;
        }
        return new string(password);
    }
}