Inifinite loop problem (easy question)

[Ulnarian]

Hey all, sorry for all the beginner's questions

Anyways, I'm trying to build a simple loop that will protect against unwanted input (i.e. when the user enters a characters instead of an integer). Here's what I have so far:

#include <iostream>
#include <cctype>

using namespace std;

int main()
{
    
    cout << "Enter a number: ";
    int number;
    cin >> number;
  
    
    while (!isdigit(number))        //Created an infinite loop!
    {cout << endl << "That is not a number, please try again: ";
     cin >> number;}
    
    cout << endl << "Enter a character: ";
    char ch;
    cin >> ch;
    
    cout << endl << number << " " << ch;
    
    int wait;
    cin >> wait;
    return 0;
}

First of all, am I correct that (!isdigit(number)) is really saying "Do this while the input is not an integer?"

Whenever I input a numeric value, say 3, I get the message stating "That is not a number, please try again"??!

Whenever I input a character value, I get an infinite loop stating" "That is not a number, please try again", and the program ignores the cin >> number within the loop.

Can anyone tell me whats wrong here?

Thanks.

[Tronfi]

Be careful. 2484 is an integer, but not a digit. I have no time to check it, sorry.

PD: You can read a char* and then check if num[i] is a digit.

[Ulnarian]

Hmmm...nevermind, this appears to be a character function. Not an integer function. I'll have to come up with a different way to do this

[suntonphon]

Hi
I think you should declare the "number" variable as char. I don know why. In another way, I would like to advise you some method to check the number which is atoi. It return 0 if the input cannot be converted to a value of that type.

correct me if t wrong
thx

[Ulnarian]

Sunton

Yeah, I think that solution works. I'll just have to remember not to use the variable as an INT later on.

Thanks

[poolisfun]

do this:

#include <iostream>
#include <cctype>

using namespace std;

int main()
{
int number;
    while(true)
{
    cout << "Enter a number: ";
    string numberS;
    cin >> numberS;
    number = atoi(numberS.c_str());
    if (itisanumber(numberS))
       break;
    else
    cout << "\nThat is not a number, please try again: ";

}
    
    cout << endl << "Enter a character: ";
    char ch;
    cin >> ch;
    
    cout << endl << number << " " << ch;
    
    int wait;
    cin >> wait;
    return 0;
}

itisanumber() function you write yourself to check if the string is a number.

[Ulnarian]

Thanks for the help everyone. I was able to find fix to the problem by using cin.clear and cin.get() to clean up my input. Here's a slightly modified version of the program:

#include <iostream>
#include <cctype>

using namespace std;

int main()
{
    
    cout << "Enter a number (or enter 77 to exit): ";  //"Lost" reference
    int number=0;
    int sum=0;
    
  
    
    while (number!=77)
{
     if (!(cin >> number))
     
     {  cout << "That is not a number. Please enter a number: ";
        cin.clear();                                  // Resets cin error flag
        cin.get();                                    // Removes bad input        
     }
     
     else if (number==77)
     break;
     
     else
     
     {    
             sum+=number;
             cout << endl << "Enter another number: ";
     }
}

    cout << endl << "Total is: " << sum;
    
    int wait;
    cin >> wait;
    return 0;
}