C++ program to convert the upper to lower and lower to upper case letter

#include<iostream>
#include<conio.h>

int main(void)
{

    int n;
    char ch;

    std::cout<<"Press any letter either upper or lower case = ";
    std::cin >> ch;

    n = ch;

    if(n >= 65 && n <= 90)
    {
        n = n + 32;
        ch = n;

        std::cout<<"The lower case of your letter is = "<<ch;
    }
    else if(n >= 96 && n <= 122)
    {
        n = n-32;
        ch = n;

        std::cout<<"The upper case of your letter is = "<<ch;
    }
    else
        std::cout<<"You pressed wrong letter";

    return 0;
}

Press any letter upper or lower case = D
The lower  case of your letter is = d