Thread: Time calculation problem

Hey there, I have been working on creating a program which calculates the number of days inbetween two dates. I have got most of the program going, but it produces some unusal results and i'm not quite sure why. Could anyone point me in the right direction?

Code:

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



long days(int sm, int sd, int sy, int em, int ed, int ey);
long factor(int mm, int dd, int yy);

int main(int argc, char *argv[])
{
int sm, sd, sy; // starting date
int em, ed ,ey; // ending date
long old;

printf("\n Calculate days between two dates .....");
printf("\n\n Enter first date in mm/dd/yyyy format: ");
scanf("%d/%d/%d",&sm,&sd,&sy);
printf("\n Enter second date in mm/dd/yyyy format: ");
scanf("%d/%d/%d",&em,&ed,&ey);
old = days(sm,sd,sy,em,ed,ey);

printf("\n There are %ld days between %d/%d/%d and %d/%d/%d\n",
old,sm,sd,sy,em,ed,ey);

system("PAUSE"); 
return 0;
}

long days(int sm, int sd, int sy, int em, int ed, int ey)
{
long fac1, fac2, elap;

fac1 = factor(sm, sd, sy);
fac2 = factor(em, ed, ey);
elap = fac2 - fac1;
return (elap);
}

long factor(int mm, int dd, int yy)
{
long xx;

xx = 365 * yy + dd + 31 * (mm - 1);
if (mm < 3)
xx = xx + ((yy -1)/4) - (.75 * ((yy - 1)/100)+1);
else
xx = xx - (.4 * mm + 2.3) + (yy / 4) - (((.75 * (yy / 100) + 1)));
return (xx);
}

Many thanks

I'm not familiar with the factor() math. Where did you get it?
Can you verify that the math is correct when you do this by hand, given the same input that the program fails on?

If you're not watching the variables in a watch window of an IDE, you may need to insert several print statements to see what's gone off the rails.

I don't see anything obvious wrong with the code itself.

Originally Posted by QuantumPete

You need proper indentation! That code is impossible to read.
Also, why don't you just convert the month, day and year into time_t and then use difftime?

QuantumPete

I tried to create a code snippet using difftime, but it didn't work. First I had to subtract 70 from the resulting years, since gmtime starts from 00:00:00 on January 1, 1970. But the struct tm starts from 1900. The snippet computed months and years correctly, but incorrect results for days.