Question

I’m trying to get user input and allowing them to only input a whole number which is also positive.

I’m trying to figure out this task

printf("Enter the first and second number in whole number: ");
scanf("%d,%d", &first, &second);

if (input != '\n') //notice this line I'm trying to check if is a character//
    printf("Error! CHARACTER NOT ACCEPTED!!\n");

else if (First <= 0)
    printf("Error! First must be a positive value!\n");

else if (Second <= 0)
    printf("Error Second must be a positive value!\n");

The code above will check for two things. One, if the user has input the characters I want. Second, if the number is positive.

How do I realize these checks?

Answer 1

You cannot restrict the characters the user inputs. You should read whatever the user gives you and decide what to do with it.

If you want to use scanf, it could be like this:

int ret = scanf("%d", &num);

scanf‘s return value shows the number of %s it successfully read. For example:

12      <-- this input returns 1, num will be 12
asd     <-- this input returns 0, num will be untouched
123xf   <-- this input returns 1, num will be 123

In the last example, xf will stay in input and further scanfs would read it.

So for the first if, you simply check if the return value of scanf is 1. If not, then you couldn’t read a number from input.

For the second if, check if num <= 0