C 基础知识，如果输入不是正的 integer，要求新的输入

Question

i am trying to make this basic program: -It asks for an input

A: if it is a positive integer, thats good, and i can use that on the second part of the program.

B: if the input is not a positive integer, it will ask for a new input until it gets a positive integer.

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

    int main()
    {
        int number;
    
        printf("Please enter a positive integer:\n");
    
        do {
                scanf("%d", &number);
    
        }
    
    
        while (number >= 0);
    
    
        return 0;
    }

Answer 1

You have the loop condition backwards - you're supposed to continue looping as long as the input is not a positive integer:

do {
    scanf("%d", &number);
}
while (number <= 0);

Answer 2

First read full lines , as invalid input (like eg letters) will not be removed from the input buffer. Then parse the input using sscanf . Then use the %u format to parse unsigned int values Lastly always check what sscanf returns .

Also remember to add a check for zero. And if the user wanted to break out of the input loop, possibly exiting the program.

Putting it together it could be something like this:

unsigned number;
char number_buffer[32];

printf("Please enter a positive integer:\n");
while fgets(number_buffer, sizeof number_buffer, stdin) != NULL)
{
    if (sscanf(number_buffer, "%u", &number) == 1 && number > 0)
    {
        // Successfully read non-negative and non-zero number, end loop
        break;
    }

    // Invalid input, ask the user again
    printf("Invalid input. Please enter a positive integer (not negative, not zero):\n");
}

if (feof(stdin) || ferror(stdin))
{
    // The user pressed the EOF keyboard-sequence, or there was an error reading
    // TODO: Handle these cases appropriately
}

I recommend you put all of this in a separate function.