int and unsignd short

This is a discussion on int and unsignd short within the C Programming forums, part of the General Programming Boards category; Hi, I made a simple function that gets and prints tomorrow's date but it doesn't work. It works only if ...

  1. #1
    Registered User
    Join Date
    Oct 2008
    Posts
    12

    int and unsignd short

    Hi,

    I made a simple function that gets and prints tomorrow's date but it doesn't work.
    It works only if I switch all "unsigned short" to regular "int".

    I think there's a problem with getting variables from "scanf". (I tried to change %d to %lu in scanf sentence but it's not working either.)

    Can anyone explain why its working only with int and how I can make it working with unsigned short?


    Code:
    #include <stdio.h>
    
    void printTomorrow(unsigned short month, unsigned short day, unsigned short year);
    bool isLeapYear(unsigned short year); //check if it's a leap year
    
    void main(void)
    {
    	unsigned short month, day, year;
    
    	printf("Input the date of which you want to know tomorrow\n");
    	printf(">> ");
    	scanf("%d %d %d", &month, &day, &year); //I inputed "7 31 2008"
    
    	printf("year: %d   month: %d   day; %d\n", year, month, day); //check if all variables are inputed correctly. it doesn't. only variable "year" has right one, rest of them has 0.
    	printTomorrow(month, day, year);
    }
    
    void printTomorrow(unsigned short month, unsigned short day, unsigned short year)
    {
    	static unsigned short lastDay[13]={0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    	if(isLeapYear(year)){	//if inputed year is leap
    		lastDay[2]=29;	//change Febrary's last day
    	}
    
    	if(month<1 || month>12 || day<1 || day>lastDay[month]) //error check
    		fprintf(stderr, "printTomorrow:: Incorrect date!\n");
    	else{
    		day++;
    		if(lastDay[month]<day){ //in case that inputed day is the last day of the month.
    			day=1;
    			month++;
    			if(month == 13){ //in case that inputed date is the last day of the year.
    				month=1;
    				year++;
    			}
    		}
    		printf("Tomorrow:: %d-%d-%d\n",month, day, year);
    	}
    }
    
    bool isLeapYear(unsigned short year)
    {
    	if(year%400 == 0)
    		return 1;
    	else if(year%4 ==0 && year%100!=0)
    		return 1;
    	else
    		return 0;
    }

  2. #2
    Kernel hacker
    Join Date
    Jul 2007
    Location
    Farncombe, Surrey, England
    Posts
    15,677
    scanf() assumes that you are telling the truth: scanf("%d", &shortUnsignedVar) will overwrite some random data after shortUnsignedVar, if the variable is the type that the name implies, as a short (in most modern compilers) is only 2 bytes long, and and int which scanf() thinks you have passed the address of is 4 bytes. If you use "%hd", scanf will store only a short, rather than a full integer.

    If you are using gcc, then you can enable full warnings with "-Wall" on the command line, and it will tell you when you "mess up" with the format and corresponding arguments for both scanf and printf type functions.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
    Registered User
    Join Date
    Oct 2008
    Posts
    12
    Thanks matsp,

    Your answer is very clear and helpful to me

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