CODEWITHSUNDEEP
c++
nakE
nakE

Reputation: 362

Is there a way I can check if user input is a number?

I make a game that the user need to guess the number,

the number is generated with rand function.

If the user wrote an invalid number or a character, print error message.

My problem is that cin.fail() does not working well for me, for example, when I enter a character as input, my program is always printing "Too Low!", maybe because it calculates the value of the character ( ASCII TALBE ).

Any suggestions ?

My Code:

void Game()
{
    srand(time(0));

    int iGuess;
    const unsigned int iNum = (rand() % 1000 + 1);

    Start:
    system("cls");

    cout << "\n Guess the Num: "; cin >> iGuess;
    if (iGuess == iNum) {
        system("color A");
        cout << "\n\n Good Job! You Won!";
        exit(0);
    }
    if (iGuess > iNum) {
        cout << "\n\n Too High!";
        Sleep(3000);
        goto Start;
    }
    if (iGuess < iNum) {
        cout << "\n\n Too Low!";
        Sleep(3000);
        goto Start;
    }
    if (cin.fail()) {
        cout << "Input has failed! & Error Code: " << GetLastError();
        Sleep(3000);
        goto Start;
    }
}

Upvotes: 2

Views: 832

Answers (3)

Picaud Vincent
Picaud Vincent

Reputation: 10982

First you can check that for streams, boolean conversion (explicit operator bool() const) is equivalent to !failed() (see https://en.cppreference.com/w/cpp/io/basic_ios/operator_bool).

This allows you to write:

void Game()
{
  srand(time(0));

  int iGuess;
  const unsigned int iNum = (rand() % 1000 + 1);

Start:
  system("cls");

  cout << "\n Guess the Num: ";
  if (cin >> iGuess)
  {
    if (iGuess == iNum)
    {
      system("color A");
      cout << "\n\n Good Job! You Won!";
      exit(0);
    }
    if (iGuess > iNum)
    {
      cout << "\n\n Too High!";
      Sleep(3000);
      goto Start;
    }
    if (iGuess < iNum)
    {
      cout << "\n\n Too Low!";
      Sleep(3000);
      goto Start;
    }
  }
  else
  {
    cin.clear();                        // clear error flags
    cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // empty buffer 
    assert(cin);                        // check that we are still in a good state

    cout << "Input has failed! & Error Code: " << GetLastError();
    Sleep(3000);
    goto Start;
  }
}

If an error happened it is important not to forget these steps:

Clear error flags:

cin.clear();

Remove all the data previously stored in the buffer (and which could not be interpreted as an integer)

cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

Check that we are still in a good state (defensive programming, another error could have happened)

assert(cin);

Update: it is certainly better to use ignore, my first version was

while (cin.get() != '\n') continue;

my update is:

cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

Upvotes: 1

Sean
Sean

Reputation: 573

I recommend utilizing the do while format to get your input. 

#include <stdlib.h>
#include <time.h>
#include <iostream>
#ifdef _WIN32
#include <windows.h>

void sleep(unsigned milliseconds)
{
    Sleep(milliseconds);
}
#else
#include <unistd.h>

void sleep(unsigned milliseconds)
{
    usleep(milliseconds * 1000); // takes microseconds
}
#endif
using namespace std;

int main()
{
    srand(time(0));

    int iGuess;
    const unsigned int iNum = (rand() % 1000 + 1);

Start:
    system("cls");

    do
    {       
        if (!std::cin)
        {
            std::cin.clear();
            std::cin.ignore(10000, '\n');
            std::cout << "\nFailed input";
        }
        std::cout << "\n Guess the Num: ";
    } while (!(std::cin >> iGuess));


    if (iGuess == iNum) {
        system("color A");
        cout << "\n\n Good Job! You Won!";
        exit(0);
    }
    if (iGuess > iNum) {
        cout << "\n\n Too High!";
        Sleep(3000);
        goto Start;
    }
    if (iGuess < iNum) {
        cout << "\n\n Too Low!";
        Sleep(3000);
        goto Start;
    }
}

Upvotes: 0

Build Succeeded
Build Succeeded

Reputation: 1150

The simplest way to parse the input string using std::string_view and std::isdigit().

char str[] = "12abc12"; 

int alphabet = 0, number = 0, i; 
for (i=0; str[i]!= '\0'; i++) 
{ 
    // check for alphabets 
    if (isalpha(str[i]) != 0) 
        alphabet++; 

    // check for decimal digits 
    else if (isdigit(str[i]) != 0) 
        number++; 
}

https://www.geeksforgeeks.org/isalpha-isdigit-functions-c-example/

Upvotes: 0

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