Answers for "playfair cipher code in c"

playfair cipher code in c

#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <ctype.h>
#define MX 5

void playfair(char ch1, char ch2, char key[MX][MX])
{
    int i, j, w, x, y, z;
    FILE *out;
    if ((out = fopen("cipher.txt", "a+")) == NULL)
    {
        printf("File Currupted.");
    }
    for (i = 0; i < MX; i++)
    {
        for (j = 0; j < MX; j++)
        {
            if (ch1 == key[i][j])
            {
                w = i;
                x = j;
            }
            else if (ch2 == key[i][j])
            {
                y = i;
                z = j;
            }
        }
    }
    //printf("%d%d %d%d",w,x,y,z);
    if (w == y)
    {
        x = (x + 1) % 5;
        z = (z + 1) % 5;
        printf("%c%c", key[w][x], key[y][z]);
        fprintf(out, "%c%c", key[w][x], key[y][z]);
    }
    else if (x == z)
    {
        w = (w + 1) % 5;
        y = (y + 1) % 5;
        printf("%c%c", key[w][x], key[y][z]);
        fprintf(out, "%c%c", key[w][x], key[y][z]);
    }
    else
    {
        printf("%c%c", key[w][z], key[y][x]);
        fprintf(out, "%c%c", key[w][z], key[y][x]);
    }
    fclose(out);
}
void main()
{
    int i, j, k = 0, l, m = 0, n;
    char key[MX][MX], keyminus[25], keystr[10], str[25] = {0};
    char alpa[26] = {
        'A',
        'B',
        'C',
        'D',
        'E',
        'F',
        'G',
        'H',
        'I',
        'J',
        'K',
        'L',
        'M',
        'N',
        'O',
        'P',
        'Q',
        'R',
        'S',
        'T',
        'U',
        'V',
        'W',
        'X',
        'Y ',
        'Z'};
    printf("\nEnter key:");
    gets(keystr);
    printf("\nEnter the plain text:");
    gets(str);
    n = strlen(keystr);
    //convert the characters to uppertext
    for (i = 0; i < n; i++)
    {
        if (keystr[i] == 'j')
            keystr[i] = 'i';
        else if (keystr[i] == 'J')
            keystr[i] = 'I';
        keystr[i] = toupper(keystr[i]);
    }
    //convert all the characters of plaintext to uppertext
    for (i = 0; i < strlen(str); i++)
    {
        if (str[i] == 'j')
            str[i] = 'i';
        else if (str[i] == 'J')
            str[i] = 'I';
        str[i] = toupper(str[i]);
    }
    // store all characters except key
    j = 0;
    for (i = 0; i < 26; i++)
    {
        for (k = 0; k < n; k++)
        {
            if (keystr[k] == alpa[i])
                break;
            else if (alpa[i] == 'J')
                break;
        }
        if (k == n)
        {
            keyminus[j] = alpa[i];
            j++;
        }
    }
    //construct key keymatrix
    k = 0;
    for (i = 0; i < MX; i++)
    {
        for (j = 0; j < MX; j++)
        {
            if (k < n)
            {
                key[i][j] = keystr[k];
                k++;
            }
            else
            {
                key[i][j] = keyminus[m];
                m++;
            }
            printf("%c ", key[i][j]);
        }
        printf("\n");
    }
    // construct diagram and convert to cipher text
    printf("\n\nEntered text :%s\nCipher Text :", str);
    for (i = 0; i < strlen(str); i++)
    {
        if (str[i] == 'J')
            str[i] = 'I';
        if (str[i + 1] == '\0')
            playfair(str[i], 'X', key);
        else
        {
            if (str[i + 1] == 'J')
                str[i + 1] = 'I';
            if (str[i] == str[i + 1])
                playfair(str[i], 'X', key);
            else
            {
                playfair(str[i], str[i + 1], key);
                i++;
            }
        }
    }
    getch();
}