Input Validation to make sure only number c++

Ok, I'm trying to get good at using pointers so I'm trying to write a input validation for the user input to make sure that anything that isn't a number is handled correctly. When I use isdigit() isn't working for me. I still get an exception when I enter a alphabet. Any suggestions? Thanks. Check this out:

#include<iostream>
#include<algorithm>
#include<string>
#include<cctype>
using namespace std;

void EnterNumbers(int * , int);


int main()
{
    int input = 0;
    int *myArray;

    cout << "Please enter the number of test scores\n\n";
    cin >> input;

    //Allocate Array
    myArray = new int[input];

    EnterNumbers(myArray,input);


    delete[] myArray;
    return 0;
}

void EnterNumbers(int *arr, int input)
{

    for(int count = 0; count < input; count++)
    {
        cout << "\n\n Enter Grade Number  " << count + 1 << "\t";
        cin >> arr[count];

        if(!isdigit(arr[count]))
        {
            cout << "Not a number";
        }
    }
}

Mats Petersson

If you test if (!(cin >> arr[count])) ... instead - isdigit(arr[digit]) tests if the value of arr[digit] is the ASCII code of a digit [or possibly matches Japanese, Chinese or Arabic (that is, as an Arabic script typeface, not that it's a 0-9 like our "Arabic" ones) digit]. So if you type in 48 to 57, it will say it's OK, but if you type 6 or 345, it's complaining that it is not a digit...

Once you have discovered a non-digit, you will also need to either exit or clean out the input buffer from "garbage". cin.ignore(1000, '\n'); will read up to the next newline or a 1000 characters, whichever happens first. Could get annoying if someone has typed in a million digits, but otherwise, should solve the problem.

You will of course also need a loop to read the number again, until a valid number is entered.

The way I do this kind of input validation is that I use std::getline(std::cin, str) to get the whole line of input and then I parse it using the following code:

std::istringstream iss(str);
std::string word;

// Read a single "word" out of the input line.

if (! (iss >> word))
    return false;

// Following extraction of a character should fail
// because there should only be a single "word".

char ch;
if (iss >> ch)
    return false;

// Try to interpret the "word" as a number.

// Seek back to the start of stream.

iss.clear ();
iss.seekg (0);
assert (iss);

// Extract value.

long lval;
iss >> lval;

// The extraction should be successful and
// following extraction of a characters should fail.

result = !! iss && ! (iss >> ch);

// When the extraction was a success then result is true.

return result;

isdigit() applies to char not to int as you're trying. The cin >> arr[count]; statement already ensures an integer numeric digits format is given in the input. Check cin.good() (!cin respectively) for possible input parsing errors.

来源：https://stackoverflow.com/questions/17982719/input-validation-to-make-sure-only-number-c

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