vigenere.c

vigenere.c

#include <stdio.h>
#include <cs50.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

int main(int argc, char *argv[])
{
        if (argc != 2)
        {
                printf("usage: %s <keyword>\n", argv[0]);
                return 1;
        }
	char* keyword = argv[1];
	int keylen = strlen( argv[1] );
	int transform;
	char* enc;

// check if keyword is all letters
	for (int i = 0; i < keylen; i++)
	{
		char letter = keyword[i];
		if (!isalpha(letter))
		{
	                printf("usage: %s <keyword>\n", argv[0]);
			return 1;
		}

	}

// magic

        printf("Input text: ");
        char* text = GetString();
        int textLen = strlen(text);
	int m = 0; // variable is used to stand against non alphabetical chars that increments i++ and at the same time breaking the cipher


	for (int i = 0; i < textLen; i++)
	{
	int textLetter = text[i];
	int modulo = (m%keylen);
	m += 1;
	int keyLetter = keyword[modulo];
	int newLetter = 0;
	if (isalpha(textLetter))
		{

		if (isupper(textLetter))
			{
				if(islower(keyLetter))
				{
					keyLetter -= 32;
					int newLetter = (textLetter + keyLetter) % 26 + 'A';
					printf("%c", newLetter);
				}
				else
				{
					int newLetter = (textLetter + keyLetter) % 26 + 'a';
					printf("%c", newLetter);
				}
			}

                if (islower(textLetter))
                	{
				textLetter -= 32;
                        if(isupper(keyLetter))
                	        {
                        		int newLetter = (textLetter + keyLetter) % 26 + 'A';
					printf("%c", newLetter);
                       		}
                        else
                        	{
					keyLetter -= 32;
               		         	int newLetter = (textLetter + keyLetter) % 26 + 'a';
					printf("%c", newLetter);
                       		}
			}
		}

	else
	{
		newLetter = textLetter;
		m -= 1;
	}


  	printf("%c", newLetter);
                }
	printf("\n");
	}