vigenere.c

vigenere.c

/*#################################### 
#vigenere.c                          # 
#Written by James Calleja, 2016      # 
#                                    # 
#Encrypts a string of text by a      # 
#cypher word provided by the user    # 
###################################### 


#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <math.h>
#include <string.h>
#include <ctype.h>

//declair global variables 
char *string;           //string to be passed in by the usere
char *cipherKey;        //holds to cipher key
char alphaLower[] = "abcdefghijklmnopqrstuvwxyz"; //an array to hold the full alphabet
char alphaUpper[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

//declair funtions 
void cipher (char*);              //cipher the text using the key pased in to the command line
char* getText ();                 //prompt user for text to pass to cipher 
int errorCheckingArgc (int);      //vet command line argument argc, must be 2
int errorCheckingArgv (char*);    //vet command line argument argv,must be postitive int
int cipherKeyToInt (char);        //convert the cipherKey[x] char to int accounting for upper and lower case
//int argvToInt (char**);         //covert the string argv[1] to an int

//main, application logic
int main (int argc, char* argv[])
{
    errorCheckingArgc(argc);
    errorCheckingArgv(argv[1]);
    cipherKey = argv[1];
    string = getText();
    cipher(string);
return 0;
}

//define functions 
int errorCheckingArgc(int argc)
{
    if (argc != 2)
    {
        printf("You have passed inproper arguments\n");
        exit(1);
    }
return 0; 
}

int errorCheckingArgv(char* argv)
{
    for (int count = 0; argv[count] != '\0'; count ++)
    {
        if (isalpha(argv[count]))
        {
            continue;
        }
        else
        {
            printf("You just fucked up son\n");
            exit(1);
        }
    }
return 0;
}

char* getText ()
{    
    char *str,c; 
    int i=0,j=1;
    str = (char*)malloc(sizeof(char));
    //printf("Enter the secret message:\n");
    while(c!='\n')
    {
        c = getc(stdin);                          //read the input from keyboard standard input
        str = (char*)realloc(str,j*sizeof(char)); //re-allocate (resize) memory for character read to be stored
        str[i] = c;                               //store read character by making pointer point to c
        i++;
        j++;
    }
    str[i]='\0';   //at the end append null character to mark end of string`
return str; 
    free(str);   //important step the pointer declared must be made free
}

int cipherKeyToInt (char cipherKey)
{
    int x;
    if (isupper(cipherKey))
    {
        x = cipherKey - 65;
    }
    else 
    {
        x = cipherKey - 97;
    }
return x; 
}

void cipher (char* string)
{
    int k = strlen(cipherKey);                      //get the length of the cipherKey
    int o = -1;                                     //set counter var for the ciperhKey
    for (int x = 0 ; string[x] != '\0'; x++ )
    {
        if(isalpha(string[x]))                      //is the ASCii value in the aplabe range
        {
            o = o + 1;                              //itterarte through the cipherKey
            int i = string[x];                      //convert char to ascii value
            if(i > 64 && i < 91)                    //check ASCii value to see if it's an upper case char
            {
                int u = o % k;                      //use mod to determind the position in the array to work with 
                int j = cipherKeyToInt(cipherKey[u]);//get the ASCii value for the oth char in the array -65 for the cipher shift
                int z = i + j;                      //move the char up the aplphabet as per cipherkey
                if(z >= 91)                         //check to see if the char needs to wrap from Z to A
                {
                    z = z - 65;                     //convert z to array position in alphaUpper[]
                    int y = (z  % 26);              //wrap around the aplabet from Z to A
                    printf("%c",alphaUpper[y]);     //print the ciphered char
                    continue;
                }
                char cipher = z;                    //convert z value back to char 
                printf("%c",cipher);                //print the ascii value char
            }
            if(i > 96 && i < 123)                   //check ASCii value to see if it's a lower case char
            {
                int u = o % k;                      //use mod to determind the position in the array to work with 
                int j = cipherKeyToInt(cipherKey[u]);//get the ASCii value for the oth char in the array -65 for the cipher shift 
                int z = i + j;                      //move the char up the aplphabet as per cipherkey
                if(z >= 123)
                {
                    z = z - 97;                     //convert z to array position in alphaLower[]
                    int y = (z % 26);
                    printf("%c",alphaLower[y]);
                    continue;
                }
                char cipher = z;                    //convert z value back to char
                printf("%c", cipher);               //print the ascii value char 
            }
        }
        else
        {
            printf("%c", string[x]);
        }
    }
}