need code to check if the value is numeric in C

I am student, taking C programming now.
I have assignment to write function to check if inputed data is numbers. if not - it should write that, and ask to enter number again.
I wrote code, to write error message, but dont know how to make program to work on next input.. should I call the Main function again ?

Code:

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int main()
{

  double hours;              //hours worked in a week
  double payrate;            // hourly salary
  double grosspay;            //total weekly payment
  int k;                          //number of values read

printf ("Enter number of hours, and hourly pay (or press 0 to exit) \n");

      while ((k = scanf ("%lf%lf", &hours, &payrate))==2)
      {

      if (isdigit(hours) !=0)
            return hours;
            else
            printf ("You entered invalid data, please enter number of hours \n");
scanf ("%lf, &hours)

      if (isdigit(payrate) !=0)
            return payrate;
            else
            printf ("You entered invalid data, please enter payrate \n");
scanf ("%lf, &payrate) 

      if (hours==0 || payrate==0)
              {
              printf ("Good Bye. \n\n");
              system("PAUSE");
              return 0;
              }

  double grosspay;
  grosspay = calculateGrossPay(hours, payrate);

  printf ("Hours worked: %.2f\n", hours);
  printf ("Hourly  Rate: %.2f\n\n", payrate);
  printf ("Your weekly payment is: $ %.2f \n\n\n", grosspay);




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I checked the page "How do i get a number from the user", but still did not understand how to fix it.. Any advice would be appreciated.
Thank you !

Quote:

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Originally Posted by mikerush7

I checked the page "How do i get a number from the user", but still did not understand how to fix it

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What's your problem with this page?

Basically you have to decide if you want to use scanf() or write your own validation function. From your assignment description it seems you have to write your own, right?
Do you know already how strings work in C and how to get them from the user?

Bye, Andreas

1. you do not call main - if you need to do it - move contents of the main into another function and then call it in the loop
2. your usage of isdigit is wrong - you do not appy it on the double. if you have a character you can use this function to check if the character is representing a digit
3. you logic is at fault - if the input does not contains 2 double values - scanf will fail - so your code inside the loop will not work in this case. you should think another way to implement the requested task

Yes, I need to write my own function. reading in the book and on internet, I found out that I need to create function that will check the number that I enter - as characters, one by one, and I need to create a loop, so it will check each character after another. I understand the idea, but I dont know, how to write the actual code..