C ++上的整数验证

Question

I have written small C++ console application and this is source code :

#include<stdio.h>
#include<locale.h>
#include<ctype.h>
#include<stdlib.h>

void main()
{
    setlocale(LC_ALL, "turkish");
    int a,b,c,d;

    printf("first number: ");
    scanf("%d", &a);

    printf("second number: ");
    scanf("%d", &b);

    c = a+b;

    printf("Sum: : %d\n", c);
}

As you can see i'm requesting two numbers from user and than summing them. But i want to add a control which check number who enterede by user is integer?

I'll check number which typed by user and than if number isn't really a integer i will echo an error. I'm using this after every scanf but it's not working very well.

if(!isdigit(a))
{
            printf("Invalid Char !");
            exit(1);
}

In shortly, on a scanf action, if user type "a" it will produce an error message and program stop working. If user type a number program will continue

Answer 1

scanf does that validation for you. Just check the return value from scanf .

printf("first number: ");
if(scanf("%d", &a) != 1) {
  printf("Bad input\n");
  return 1;
}

printf("second number: ");
if(scanf("%d", &b) != 1) {
  printf("Bad input\n");
  return 1;
}

Answer 2

The C++ way to do this would be

#include <iostream>
#include <locale>

int main()
{
    std::locale::global(std::locale("nl_NL.utf8")); // tr_TR doesn't exist on my system

    std::cout << "first number: ";

    int a;
    if (!(std::cin >> a))
    {
        std::cerr << "whoops" << std::endl;
        return 255;
    }

    std::cout << "second number: ";

    int b;
    if (!(std::cin >> b))
    {
        std::cerr << "whoops" << std::endl;
        return 255;
    }

    int c = a+b;

    std::cout << "Sum: " <<  c << std::endl;

    return 0;
}

Answer 3

isdigit takes a char as an argument.

If the call to scanf succeeds, you're guaranteed that you have an integer.

scanf also has a return value which indicates how many values it has read.

You want to check if the return value of scanf is 1 in this case.

See: http://www.cplusplus.com/reference/clibrary/cstdio/scanf/