c++ validate input value before add it to array - c++

Question

My target is to validate input value before add it into array. Current code used:
int main()
{
int temp;
int arr[5];
for(int i = 0; i < 5; i++)
{
// validate here
cin >> arr[i];
}
return 0;
}
and my validation method:
int validateInput(string prompt)
{
int val;
while (true)
{
cin.clear();
cin.sync();
cout << prompt;
cin >> val;
if (cin.good() && val >= -50 && val <= 50)
{
break;
}
else
cin.clear();
cout << "Invalid input! number must be between -50 and 50" << endl;
}
return val;
}
How is that possible?

Answer 1

Your validateInput should just deal with validation: it should answer "is x valid or not valid?"
bool validateInput(int x)
{
return val >= -50 && val <= 50;
}
When reading from stdin, use validateInput and branch accordingly:
for(int i = 0; i < 5; i++)
{
int temp;
cin >> temp;
if(cin.good() && validateInput(temp))
{
arr[i] = temp;
}
else
{
cout << "Invalid input! number must be between -50 and 50" << endl;
// handle invalid input
}
}
If you want to further abstract the idea of "only reading valid numbers from std::cin", you can use an higher-order function:
template <typename TFValid, typename TFInvalid, typename TFInvalidIO>
decltype(auto) processInput(TFValid&& f_valid, TFInvalid&& f_invalid, TFInvalidIO&& f_invalid_io)
{
int temp;
cin >> temp;
if(!cin.good())
{
// Invalid IO.
return std::forward<TFInvalidIO>(f_invalid_io)();
}
if(validateInput(temp))
{
// Valid IO and datum.
return std::forward<TFValid>(f_valid)(temp);
}
// Valid IO, but invalid datum.
return std::forward<TFInvalid>(f_invalid)(temp);
}
Usage:
for(int i = 0; i < 5; i++)
{
processInput([&](int x){ arr[i] = x; },
[](int x){ cout << x << " is invalid"; },
[]{ cout << "Error reading from cin"; });
}
If you want more genericity you can also pass validateInput and the type of input as an additional parameters.

Answer 2

Vittorio's answer above is spot on. For completeness, if you want exactly 5 elements:
#include <string>
#include <iostream>
using namespace std;
bool validateInput(int inValue)
{
return inValue >= -50 && inValue <= 50;
}
int main()
{
int _arr[5];
int _currentIdx = 0;
int _tmp;
while (_currentIdx < 5)
{
cin >> _tmp;
if (validateInput(_tmp))
{
_arr[_currentIdx] = _tmp;
_currentIdx++;
}
else
{
cout << "Invalid input! number must be between -50 and 50" << endl;
}
}
}

Answer 3

replace
cin >> temp;
with
arr[i] = validateInput("some str");