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Recently one of my beginner C++ developers-friends showed me a non-industrial piece of code where he wanted to learn entities of loops, std::cin, and std::cout concepts. Let me introduce a problem briefly. He has to enter via std::cin the number of numbers that he needs to insert from the keyboard in order to count the average of that numbers. Here is the code(please do not be critical to the code).

#include <iostream>

int main ()
{
    int amount = 0;
    
    std::cout << "Please insert amount of numbers you want to enter"<<'\n';
    
    std::cin >> amount;
    
    std::cout << "You have to enter "<< amount <<" numbers"<<'\n';
    
    if (amount < 1){
        std::cout << "You entered invalid number" << '\n';
        
        std::cout << "Average is "<< 0.0 <<'\n';
    }
    else{
            float current = 0.0;
            
            float total_sum = 0.0;
            
            for ( int i = 1; i <= amount; ++i){
                
                std::cout << "Insertion " << i <<": Please enter any number" << '\n';
                std::cin >> current;   
                total_sum += current;
            }
            std::cout << "Average is " << total_sum/amount << '\n';
        }
    return 0;
}

The code works fine when we insert integer values via std::cin for the amount variable, but whenever we enter any floating-point number for amount the code starts doing strange things. For example here is the behavior when I inserted 3.14

Please insert amount of numbers you want to enter
3.14
You have to enter 3 numbers
Insertion 1: Please enter any number
Insertion 2: Please enter any number

I even checked for extra convenience what value will be assigned to amount in such cases, and the result is predictable that it will narrow the value and assign it to the variable. Unfortunately, I couldn't find an explanation to this issue and hope I can do it with your assistance.

Hayk Manukyan
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  • Why are you attempting to enter a `float`? What did you expect to happen when you entered something that wasn't an `int`? – PaulMcKenzie Oct 31 '21 at 08:54
  • Entering float is not a good idea, but even if I do it I think it shouldn't behave like this, it narrows the value, so no problem should be, especially if that fragment of code where misbehaving occurs – Hayk Manukyan Oct 31 '21 at 08:59
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    [cin.fail](https://stackoverflow.com/questions/17928865/correct-way-to-use-cin-fail). The input expects a digit, not a `.` character. So now what is the stream going to do when it sees that character? Jump over it and start with the `1`? (the stream is still in a fail state). – PaulMcKenzie Oct 31 '21 at 09:02
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    Once you have read `3` as an integer, the remaining input stream is `.14`. Then you try to read that as an integer. – molbdnilo Oct 31 '21 at 09:07
  • **You have to enter 3 numbers** is the result `std::cout << "You have to enter "<< amount <<" numbers"<<'\n';` statement, so it means `amount` became 3, and the program should go on in a normal way, shouldn't it? – Hayk Manukyan Oct 31 '21 at 09:07
  • Thank you guys, I understand whats the problem. – Hayk Manukyan Oct 31 '21 at 09:09

0 Answers0