In c++ how to make only one cin number allowed?

Question

I am new to programming. I wrote the following as a practice. From what I wrote the cin/s can be any numbers. But I want to make the cin/s only accept certain numbers. Please help!

Please see the following:

#include <iostream>

using namespace std;

main(){
    
    int a;
    float c, d;
    c = 115.5;
    d = 57.75;
    a = 57;
    
    cout << "What is 65 + 50.5?"<<endl;
    cin>> c;
    cout << "Now make the result in half."<<endl;
    cin>> d;
    cout << "Great. What will remain when you take the 0.75 out?"<<endl;
    cin>> a;
   
}

Answer 1

Well, after you read your variable via std::cin, then you have to check their values.

E.g. the following code keeps reading as long as the user doesn't enter a number between 1 and 100

#include <iostream>

int main()
{
    int number;
    do
    {   std::cout << "Please, enter a number between 1 and 100 (inclusive): ";
        std::cin >> number;
    } while (number < 1 || number > 100);
    
    std::cout << "You entered: " << number << std::endl;
    
    return 0;
}

Does this help?