Member Avatar for HugoRocha

I need a way to convert a variable to an int or to ascii code, tried atoi, static_cast, didnt work very well... The objective is to detect if the user inserted any character other than a number, a number smaller than 0 or larger than 5, and send a message if so...
Here is the program with one of my tries...

#include<cstdlib>
#include<cstdio>
#include<iostream>

using namespace std;

int main()
{
    while(1)
    {
         back:
         cout << "Insert two numbers" << endl;
         int num1, num2;
         cin >> num1 >> num2;
         int a = static_cast<int> (num1);
         int b = static_cast<int> (num2);
         if ( ( a <= -1 ) || ( a > 5 ) || ( b <= -1 ) || ( b > 5) )
         {
                cout << "Incorrect input" << endl;
                goto back;
         }
         if ( fim(tabuleiro) )  break; //please dont mind this, this is a small part of a bigger program
    }
}

Please note that im quite new at programing so if anyone has any tips i would apreciate it =)
Thank You.

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Dani AI

Generated

A reliable pattern for this kind of validation is to read a full input line and then parse it. That way the program can detect non-numeric characters, missing or extra tokens, and still perform range checks (0..5). Reading with std::getline into a std::string and then using std::istringstream keeps cin clean and makes it straightforward to reject malformed input.

#include <iostream>
#include <string>
#include <sstream>

bool readTwoIntsInRange(int &a, int &b, int minv, int maxv)
{
    std::string line;
    if(!std::getline(std::cin, line)) // EOF or error
        return false;

    std::istringstream iss(line);
    if(!(iss >> a >> b))               // not two integers
        return false;

    char extra;
    if(iss >> extra)                   // extra non-space input found
        return false;

    return (a >= minv && a <= maxv && b >= minv && b <= maxv);
}

int main()
{
    int x, y;
    while(!readTwoIntsInRange(x, y, 0, 5))
        std::cout << "Incorrect input\n";
    // validated x and y here
}

This addresses the issues raised in the thread: is right that casting the already-int values is unnecessary; is mistaken to imply characters cannot be typed (typing letters will cause parsing to fail); and 's idea of checking the stream state is on the right track, but the getline+istringstream approach tends to be simpler and less error-prone. Extra notes: handle EOF if needed, and adapt the check if single-digit-only input (0..5) is required (e.g., reject multi-digit numbers like 12).

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Member Avatar for twomers

Why do you need to cast or even make a and b? Just test num1 and num2:

using namespace std; 
int main()
{
    while(1)
    {
         int num1, num2;
         cout << "Insert two numbers" << endl;
         cin >> num1 >> num2;
         if ( ( num1 <= -1 ) || ( num1 > 5 ) || ( num2 <= -1 ) || ( num2 > 5) )
         {
                cout << "Incorrect input" << endl;
         }
    }
}
Member Avatar for HugoRocha

Hum, what if the user inserts a character or something else? Shouldnt be able to compare with an int should it?

Member Avatar for hacker9801

...
num1 is already of int type, you WOULDN'T be able to enter a character anyway.

commented: a char is an 8-bit integer. get your basic facts straight before "helping" please +0
Member Avatar for Nick Evan

...
num1 is already of int type, you WOULDN'T be able to enter a character anyway.

Why not? Just press something on the keyboard.

It would be a good idea to check wether the input is int or not.
Perhaps something like:

using namespace std; 
int main()
{
    while(1)
    {
         int num1, num2;
         cout << "Insert two numbers" << endl;
         cin >> num1 >> num2;
         cin.ignore(numeric_limits<int>::max(), '\n');
         if (!cin || cin.gcount() != 1)
            cout << "Not a number\n";

         else if ( ( num1 <= -1 ) || ( num1 > 5 ) || ( num2 <= -1 ) || ( num2 > 5) )
               cout << "Incorrect input" << endl;
    }
}

That should take care of invalid input. Didn't test it though

[edit] and don't forget to #include <limits>

Member Avatar for HugoRocha

Worked out great, thanks a lot ;)
Really helpful =D
Exactly what i wanted...

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