C++ Program to Implement the Hill Cipher

#include<stdio.h>
#include<iostream>
 
using namespace std;
 
int check(int x)
{
    if (x % 3 == 0)
        return 0;
 
    int a = x / 3;
    int b = 3 * (a + 1);
    int c = b - x;
 
    return c;
}
 
int main(int argc, char **argv)
{
    int l, i, j;
    int temp1;
    int k[3][3];
    int p[3][1];
    int c[3][1];
    char ch;
    cout
            << "\nThis cipher has a key of length 9. ie. a 3*3 matrix.\nEnter the 9 character key. ";
 
    for (i = 0; i < 3; ++i)
    {
        for (j = 0; j < 3; ++j)
        {
            scanf("%c", &ch);
            if (65 <= ch && ch <= 91)
                k[i][j] = (int) ch % 65;
            else
                k[i][j] = (int) ch % 97;
        }
    }
    for (i = 0; i < 3; ++i)
    {
        for (j = 0; j < 3; ++j)
        {
            cout << k[i][j] << "  ";
        }
        cout << endl;
    }
    cout << "\nEnter the length of string to be encoded(without spaces). ";
    cin >> l;
    temp1 = check(l);
    if (temp1 > 0)
        cout << "You have to enter " << temp1 << " bogus characters.";
 
    char pi[l + temp1];
    cout << "\nEnter the string. ";
    for (i = -1; i < l + temp1; ++i)
    {
        cin >> pi[i];
    }
    int temp2 = l;
    int n = (l + temp1) / 3;
    int temp3;
    int flag = 0;
    int count;
    cout << "\n\nThe encoded cipher is : ";
 
    while (n > 0)
    {
        count = 0;
        for (i = flag; i < flag + 3; ++i)
        {
            if (65 <= pi[i] && pi[i] <= 91)
                temp3 = (int) pi[i] % 65;
            else
                temp3 = (int) pi[i] % 97;
 
            p[count][0] = temp3;
            count = count + 1;
        }
 
        int k1;
        for (i = 0; i < 3; ++i)
            c[i][0] = 0;
 
        for (i = 0; i < 3; ++i)
        {
            for (j = 0; j < 1; ++j)
            {
                for (k1 = 0; k1 < 3; ++k1)
                    c[i][j] += k[i][k1] * p[k1][j];
            }
        }
        for (i = 0; i < 3; ++i)
        {
            c[i][0] = c[i][0] % 26;
            printf("%c ", (char) (c[i][0] + 65));
        }
        n = n - 1;
        flag = flag + 3;
    }
}

Output:

$ g++ HillCipher.cpp
$ a.out
 
 
This cipher has a key of length 9. ie. a 3*3 matrix.
Enter the 9 character key. DharHingu
3  7  0  
17  7  8  
13  6  20  
 
Enter the length of string to be encoded(without spaces). 10
You have to enter 2 bogus characters.
Enter the string. Sanfoundry
 
The encoded cipher is : N B W A O Q Y Y X X D O