what is my mistake

Code:

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#include <cs50.h>
#include <stdio.h>

int
main(void)
{
    int days = 0;
    do {
        // user is promted to enter number of days in his month
        printf("Enter number of days in the month: ");
        days = GetInt();
        // program shows number of days entered
        printf("You entered %d days.\n" , days);
        // repeat if input is not 28, 29, 30 or 31
    ) while (31 < days < 28);
}

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compiler is gcc on fedora and I get this error when compiling

make: warning: Clock skew detected. Your build may be incomplete.

I've had this warning before, and AFAIK, it makes no difference in the final program.

Also, your program is incorrect:
- main should return a number (usually 0) at the end
- you're using ")" instead of "}" on line 15

Check again line #15, is your condition written correctly?

EDIT: If not sure, revise C's operators and their uses

Your system clock might be skewed. I always recommend installing the ntp package to keep your system clock synchronized to time servers.

Also the test in the while loop doesn't do what you expect.

'make' works by mod times of files. man make.

Quote:

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The make program uses the makefile data base and the last-modification times of the files to decide which of the files need to be updated.

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Check your system and file times using 'date' and 'ls -la $filename'. If your $filename mod time is off but system time is OK, 'touch $filename'. Also, you can compile with 'gcc -Wall $filename' and the warning should disappear?

christop suggestion of ntp is a good idea.

Code:

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while(31 < days < 28);

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Shouldn't this be

Code:

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while(31 < days && days < 28);

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Quote:

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Originally Posted by Click_here

Shouldn't this be

Code:

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while(31 < days && days < 28);

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So, execute the loop forever?

I kid, I kid. OP needs to change the comparison operators around.

Quote:

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Originally Posted by Click_here

Code:

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while(31 < days < 28);

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Shouldn't this be

Code:

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while(31 < days && days < 28);

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Nope. That will never be true. Actually, it should be:

Code:

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while (days > 31 || days < 28);

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Quote:

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Nope. That will never be true. Actually, it should be:...

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OP has wrong logic in there and written incorrectly. Your way is right.

31 < days < 28 would make more sense being
NOT(31 >= days >= 28) -> "Loop when it is not in this domain"

= !((31>=days) && (days >= 28))
= ! (31>=days) || !(days >= 28)

= (31<days) || (days < 28)