Question

I want to use the following code just to check the input.

#include <stdio.h>
#include <iostream>
#include <ctype.h>

int main() 
  {
    int number1; 

    puts("Enter number 1 please:");
    scanf_s("%d",&number1);

    if (isdigit(number1)) 
    {
      puts("Input is correct.");

    }
    else 
    {
      puts("Your input is not correct. Enter a number please.");
    }

      std::cin.get();
      std::cin.get();


  }

Unfortunately it doensn’t work. I type in a digit and my response is “Your input is not…”. Any suggestions where the problem is?

Answer 1

Your problem is in the use of isdigit. Compare this code:

int main() 
{
int number1; 

puts("Enter number 1 please:");
scanf_s("%d",&number1);
printf("You entered %d\n", number1);
if (isdigit(number1)) 
{
  puts("Input is correct.");

}
else 
{
  puts("Your input is not correct. Enter a number please.");
}

  std::cin.get();
  std::cin.get();


}

When you enter a valid number, this is reflected in the successful printf of this number.

You should check the return of scanf, not use isdigit, such as this sample code:

int main() 
{
int number1; 

puts("Enter number 1 please:");
if (scanf_s("%d",&number1))        
  puts("Input is correct.");
else
  puts("Your input is not correct. Enter a number please.");

std::cin.get();
std::cin.get();
}

I believe that for more than one field, you will need to check the return value of scanf more closely than simply zero or one.