c - Am I calling this function wrong? -

i writing program figure out elapsed time between 2 given times.

for reason, getting error: expected identifier or 'c' in regards elapsedtime function prototype before main function.

i have tried moving around program , doesn't make difference if locate after t1 , t2 have been declared. what's problem?

thank you

#include <stdio.h>  struct time {   int seconds;   int minutes;   int hours; };  struct elapsedtime(struct time t1, struct time t2);  int main(void) {      struct time t1, t2;      printf("enter start time: \n");     printf("enter hours, minutes , seconds respectively: ");     scanf("%d:%d:%d", &t1.hours, &t1.minutes, &t1.seconds);      printf("enter stop time: \n");     printf("enter hours, minutes , seconds respectively: ");     scanf("%d:%d:%d", &t2.hours, &t2.minutes, &t2.seconds);      elapsedtime(t1, t2);      printf("\ntime difference: %d:%d:%d -> ", t1.hours, t1.minutes, t1.seconds);     printf("%d:%d:%d ", t2.hours, t2.minutes, t2.seconds);     printf("= %d:%d:%d\n", differ.hours, differ.minutes, differ.seconds);      return 0; }  struct elapsedtime(struct time t1, struct time t2) {     struct time differ;      if(t2.seconds > t1.seconds)     {         --t1.minutes;         t1.seconds += 60;     }      differ.seconds = t2.seconds - t1.seconds;      if(t2.minutes > t1.minutes)     {         --t1.hours;         t1.minutes += 60;     }      differ.minutes = t2.minutes - t1.minutes;     differ.hours = t2.hours - t1.hours;      return differ; } 

your function doesn't define return type:

struct elapsedtime(struct time t1, struct time t2); 

struct not enough define return type. need struct name well:

struct time elapsedtime(struct time t1, struct time t2); 

you need assign return value of function something:

struct time differ = elapsedtime(t1, t2); 

with working, logic "borrowing" when doing difference backwards:

if(t1.seconds > t2.seconds)     // switched condition {     --t2.minutes;               // modify t2 instead of t1     t2.seconds += 60; }  differ.seconds = t2.seconds - t1.seconds;  if(t1.minutes > t2.minutes)     // switched condition {     --t2.hours;                 // modify t2 instead of t1     t2.minutes += 60; } 

as is, if t1 after t2, hour negative. if assume means end time following day, add 24 hours:

if(t1.hours > t2.hours) {     t2.hours+= 24; }  differ.hours= t2.hours - t1.hours;