为什么 printf 只打印一个空白

Question

I've been trying to figure the problem but after 3 hours I quit, anyone have any suggestion how this problem might occur. Any help would be appreciated. Currently using codeblock 20.23. img of the empty blank

#include <stdio.h>
#include <stdbool.h>
int main()
{
    int dd, mm, yy, temp = 0;
    bool isLeapYear = temp;
    printf("Enter the year: ");
    scanf("%d", &yy);
        if(yy < 0)
        {
        printf("Year number cannot be smaller than 0!");
        return 0;
        } else
        {
            if(yy%4==0 && yy%400==0 || yy%4==0)
            temp = 1;
        }
    printf("Enter the month: ");
    scanf("%d", &mm);
        if(mm > 12 || mm < 0)
        {
        printf("Month number cannot be smaller than 0 or bigger than 12!");
        return 0;
        }
    printf("Enter the date: ");
    scanf("%d", &dd);
        if(dd > 30 || dd < 0)
        {
        printf("Date number cannot be smaller than 0 or bigger than 30!");
        return 0;
        } else
        {
            if(dd == 29 && mm == 2 && temp == 0)
            printf("Since given year is not a leap year therefore your input date is invalid.");
            return 0;
        }
    printf("dd/mm/yy of your given number: %02d/%02d/%04d", dd, mm, yy);
    return 0;

}

Answer 1

Did you forget to block correctly?

if(dd == 29 && mm == 2 && temp == 0){
  printf("Since given year is not a leap year therefore your input date is invalid.");
  return 0;
}

instead of

if(dd == 29 && mm == 2 && temp == 0)
  printf("Since given year is not a leap year therefore your input date is invalid.");
  return 0;

Answer 2

If we indent the code properly we see that the last if-statement looks like this:

if (dd > 30 || dd < 0) {
    printf("Date number cannot be smaller than 0 or bigger than 30!");
    return 0;
} else {
    if (dd == 29 && mm == 2 && temp == 0)
        printf("Since given year is not a leap year therefore your input date is invalid.");
    return 0;
}

This means that the return statement in the else-clause is always executed for a valid day and hence the final print statement is never executed. You should also print to the standard error stream (with a newline) and return an error code (instead of zero which means success):

fprintf(stderr, "...\n");
return 1;