C program to print up-time in hours,minutes and seconds.

Question

I made this program to print up time in hours,minutes and seconds

#include<stdio.h> int main() { float a, b,x,mina,minb,hrsa,hrsb; float seca,secb; FILE *fp = fopen("/proc/uptime", "r"); fscanf(fp, "%f %f", &a, &b); seca=(a)%60; mina=seca/60; hrsa=mina/60; secb=(b)%60; minb=secb/60; hrsb=minb/60; printf("Uptime=%f hrs %f min %f sec",hrsa,mina,seca); printf("Idealtime =%f hrs %f min %f sec",hrsb,minb,secb); return 0; }

here i am getting an error "invalid operands to binary" in lines 12 and 16.

AShelly · Accepted Answer · 2012-03-14 19:23:34Z

2

You can't do mod (%) on floats. Try ((long)a)%60; Or even (long long), but the 68 years that 1<<31 seconds provides should be sufficient....

Also, you need another mod operation on minutes, or else 3601 seconds becomes "1 hour 60 minutes, 1 second", instead of "1 hour 0 minutes, 1 second".

edited Mar 14, 2012 at 19:23

answered Mar 14, 2012 at 18:23

AShelly

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5 Comments

Tomas Pruzina Over a year ago

I don't see any appearant bonus from using long long, care to explain? (I know about rounding and x86 representation of floats, but in this case it just does not make sense to me).

AShelly Over a year ago

I was just thinking about the fact that FLOAT_MAX is 1E38 while LONG_MAX is 4E9. I didn't do the math to realize that 4e9 seconds is 136 years, and therefore long should be sufficient.

Hasturkun Over a year ago

What you can do, though, is call fmodf or (in C99) remainderf, which will return the floating point remainder

user1263375 Over a year ago

((long)a)) did worked.I have never used this in C.Can you please explain how this work?

AShelly Over a year ago

It is a typecast. It essentially forces the complier to convert a into a long before the operation. You could think of it as doing long temp = a; seca = temp%60;

user851031 · Accepted Answer · 2012-03-14 18:26:06Z

You can't take a modulus of a float (What is the remainder of 5.5/3? Doesn't make sense).

By the way, /proc/uptime returns values which are already in seconds so seca should be

seca=(long)(a);

user677656 · Accepted Answer · 2012-03-14 18:26:26Z

0

a and b are float, they should be int

answered Mar 14, 2012 at 18:26

user677656

Comments

Tomas Pruzina · Accepted Answer · 2012-03-14 18:27:01Z

Unless you have to do this by hand, take a look at standard time functions.

man time.h

To your code (as others noted) you can't really do integer division and integer mod operation on floats (makes no sense whatsoever).

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C program to print up-time in hours,minutes and seconds.

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