Playfair Cipher Encryption in C++

//playfair_cipher
#include <iostream>
#include <string>
#include <cstdio>
#include <cctype>
#include <map>
#include <utility>
using namespace std;
#define siz 5
map <char, int> mp;
pair<int, int> p1;
pair<int, int> p2;
map < char, pair<int, int> > pa;
char a[siz][siz], res[siz][siz];
string as="ABCDEFGHIJKLMNOPQRSTUVWXYZ";

bool ischar(char c){
    if((c>='a' && c<='z') || (c>='A' && c<='Z'))
        return true;
    return false;
}

int main()
{
    string key, message, msg;
    //freopen("input.txt", "r", stdin);
    while(getline(cin, key)){
        int k = 0, l = 0;
        int len = key.size();
        for(int i=0;i<len;i++){
            if(ischar(key[i])) {
                if(mp[toupper(key[i])] == 0) {
                    a[k][l] = toupper(key[i]);
                    pa.insert(make_pair(toupper(key[i]), make_pair(k, l)));
                    mp[toupper(key[i])] = 1;
                    l++;
                }

                if(l==5) {
                    k++;
                    l = 0;
                }
            }
        }
        //mp['J'] = 1;

        for(int i=0; i<as.size();i++){
            if((toupper(as[i])=='I'||toupper(as[i])=='J') && (mp['I'] == 1||mp['J'] == 1))
                continue;
            if(mp[toupper(as[i])] == 1)
                continue;
            else {
                a[k][l] = toupper(as[i]);
                pa.insert(make_pair(toupper(as[i]), make_pair(k, l)));
                l++;
            }

            if(l==5) {
                k++;
                l = 0;
            }
        }

        //printing the grid
        for(int i=0; i<5; i++) {
            for(int j=0; j<5; j++) {
                if(j) cout<< " ";
                cout << a[i][j];
                res[i][j]='0';
            }
            puts("");
        }

        //get the message
        getline(cin, msg);
        cout<<msg<<endl;

        for(int i=0; i<msg.size(); i++)
            if(ischar(msg[i]))
                message += msg[i];

        for(int i=0; i<message.size()-1; i++) {
            char x,y;

            if(message[i] != message[i+1]) {
                x = toupper(message[i]);
                y = toupper(message[i+1]);

                p1 = pa.find(x)->second;
                p2 = pa.find(y)->second;
                i += 1;
            } else {
                x = toupper(message[i]);
                y = 'X';
                p1 = pa.find(x)->second;
                p2 = pa.find(y)->second;

            }

            //columns are same
                if(p1.second == p2.second) {
                    if(p1.first+1 < 5)
                        cout << a[p1.first + 1][p1.second];
                    else
                        cout << a[0][p1.second];

                    if(p2.first+1 < 5)
                        cout << a[p2.first + 1][p2.second];
                    else
                        cout << a[0][p2.second];
                } else if(p1.first == p2.first) { //rows are same
                    if(p1.second+1 < 5)
                        cout << a[p1.first][p1.second + 1];
                    else
                        cout << a[p1.first][0];

                    if(p2.second+1 < 5)
                        cout << a[p2.first][p2.second + 1];
                    else
                        cout << a[p2.first][0];
                } else {
                    cout    << a[p1.first][p2.second]
                            << a[p2.first][p1.second];
                }
                printf(" ");
        }

        //clearing
        mp.clear();
    }
    return 0;
}