encryption

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<bits/stdc++.h>
using namespace std;

char str[100];
int modInverse(int a, int m)
{
    a %= m;
    for(int x = 1; x < m; x++)
    {
        if((a*x) % m == 1) return x;
    }
}

void encrypt()
{
    getchar();
    int k1,k2,c,p,x,y,z;
    k1=7;
    k2=2;
    cout<<"Please type your plaintext:  "<<endl;
    gets(str);
    for(int i=0; i<strlen(str); i++)
    {
        if(str[i]==' ') cout<<" ";
        else
        {
            p=str[i]-'a';
            p=p*k1;
            p=p+k2;
            p%=26;
            cout<<char(p+97);
        }
    }
    cout<<endl;
}

void decrypt()
{
    getchar();
    int k1,k2,c,p,x,y,z;
    k1=7;
    k2=2;
    cout<<"Please type your ciphertext: "<<endl;
    gets(str);
    for(int i=0; i<strlen(str); i++)
    {
        if(str[i]==' ') cout<<" ";
        else
        {
            p=str[i]-'a';
            p=p+(26-k2);
            c=modInverse(k1,26);
            p=p*c;
            p=p%26;
            cout<<char(p+97);
        }
    }
    cout<<endl;
}



int main()
{
    cout<<"Welcome to Assoscrypto system "<<endl;
    char ch;
    while(1)
    {
        cout<<"What do you want to perform? (encryption=e, decryption=d): "<<endl;

        cin>>ch;

        if(ch=='e') encrypt();
        else decrypt();
        cout<<"Do you want to continue ? (yes=y, no=n)"<<endl;
        cin>>ch;
        if(ch=='n')
        {
            cout<<"Thank you "<<endl;
            break;
        }

    }
    return 0;
}