C: Output "tomorrow's date"

Question

I'm a code golf novice, but I'm eager to give it a go.

My challenge is: Write the shortest program in C which takes in a date D as input and outputs the date D + 1 day

Rules:

• program must compile only with gcc progname.c -o progname So no compiler/makefile tricks (if there are any) - compiler warnings don't matter
• The input and output format must be day/month/year zero padding of single digit values does not matter: 1/3/1998 is equal to 01/03/1998
• It doesn't matter how you give the the program it's input date, it can be a program argument, scanf whatever. Output must be to stdout however
• February has 29 days when the year is divisible by 4
• No date validation necessary, i.e. assume the input is always a valid date.
• any integer year should be supported, i.e. INT_MIN -> INT_MAX

Shortest code length wins, and there are extra points for extra bastardised C.

My solution uses 126 123* 121 characters

Good luck

*s="%i/%i/%i",m,d;main(y){scanf(s,&d,&m,&y);printf(s,d,m,(d=d%((m>7^m&1)+27+(m-2?3:y%4?1:2))+1)-1?y:(m=m%12+1)-1?y:y+1);}

*because of an idea Gareth's code gave me

Answer 1

Okay, it's been a while since I wrote any C but I'll give it a go:

m,y,*q="%d/%d/%d";
main(d){
scanf(q,&d,&m,&y);
++d>30+(m+(m>7))%2-(m^2?0:2-!(y%4))?(m+=d=1)>12?y+=m=1:0:0;
printf(q,d,m,y);}

120 characters.
With a bit of formatting(not that it makes it any more readable any more...):

m,y,*q="%d/%d/%d";
main(d)
{
    scanf(q,&d,&m,&y);
    ++d>30+(m+(m>7))%2-(m^2?0:2-!(y%4))?(m+=d=1)>12?y+=m=1:0:0;
    printf(q,d,m,y);
}

The compiler throws out warnings like nobody's business, but it works.

I'm not sure I can get it any smaller than this now without stealing a couple of tricks from Griffin. With those tricks I can get to 116 characters:

m,y,*q="%d/%d/%d";
main(d){
scanf(q,&d,&m,&y);
printf(q,d,m,++d>30+(m>7^m&1)-(m^2?0:2-!(y%4))?(m+=d=1)>12?y+=m=1:y:y);}

Answer 2

C, 112 chars

Many months late, but I just saw it and decided to improve it.
The leading * isn't needed for 32bit platforms (and some 64bit platforms), so it can perhaps be removed.

*s="%d/%d/%d";
main(y,m,d){
    scanf(s,&d,&m,&y);
    d++>29+(m-2?m+m/8&1:!(y%4)-2)?d=m++<12||(y+=m=1):0;
    printf(s,d,m,y);
}

Lots of similarity to Gareth's solution, but honestly - I didn't look.
The only thing I did borrow was saving the format string in a variable (which is kind of obvious, but I missed it).

I do fix a problem with Gareth's solution - it relies on the evaluation order of printf parameters.

Answer 3

C - 293

#define w(x) while(*(i++)!='/');x=atoi(i);
main(){char x[99];scanf("%s",x);f(x);}
f(char* i){
int a=atoi(i),b,c,m[]={0,1,0,1,0,1,0,1,1,0,1,0,1};
w(b);w(c);
if(b==2)if((a==28&&c%4)||a==29){a=1;b=3;}else a++;else if(a-m[b]-30==0)if(b==12){a=b=1;c++;}else{a=1;b++;}else a++;
printf("%d/%d/%d",a,b,c);}

I've never really tried to golf C (and I am by no means an expert in C), but I feel this is pretty good. Basically it goes like this: get input from scanf, convert days, shift pointer, convert months, shift pointer, convert years (latter two have a #define to help), do logic with calendar logic. year%4 was a cool trick, and I have a month hash table indicating if the month is 30 or 31 days (kinda big to declare, but I think it was worth it). Finally, print. I'm sure there is a neat way to refactor using ternary (?:), but again, I'm no expert.

EDIT: fixed some typos.

Answer 4

C (in a way), 97 71

I will lose fifty rep for this but it was necessary.

The actual rule violation is that it doesn't quite do INT_MIN..INT_MAX; the range instead seems to be 0..1410065407 (on 64-bit Ubuntu 11... I'm saying nothing about portability :P).

main(){system("read a;date -d@$((`date -d$a +%s`+86400)) +%m/%d/%Y");}

(old version:)

d,e[9];main(){sprintf(e,"date -d@$((`date -d%s +%%s`+86400)) +%%m/%%d/%%Y",gets(&d))&system(e);}

Answer 5

106 100 characters

Another entry that breaks the year rule by supporting only the years 1 to 9999, and also implements correct leap year handling instead of following requirements. The code simply uses POSIX libraries while abusing the type system:

t[9],b[9],*f="%d/%m/%Y";main(){gets(b);strptime(b,f,t);t[3]++;mktime(t);strftime(b,99,f,t);puts(b);}