C program to calculate the time difference between 2 time stamps

#include <time.h>
#include <stdio.h>

int main(void)
{
struct tm str_time;
time_t time_of_day;

struct tm str_time1;
time_t time_of_day1;
       
       
str_time.tm_year = 2012; //-1900;
str_time.tm_mon = 6;
str_time.tm_mday = 5;
str_time.tm_hour = 10;
str_time.tm_min = 3;
str_time.tm_sec = 5;
str_time.tm_isdst = 0;

str_time1.tm_year = 2017-1900;
str_time1.tm_mon = 1;
str_time1.tm_mday = 1;
str_time1.tm_hour = 1;
str_time1.tm_min = 1;
str_time1.tm_sec = 1;
str_time1.tm_isdst = 0;

time_of_day = mktime(&str_time);
printf(ctime(&time_of_day));

time_of_day1 = mktime(&str_time1);
printf(ctime(&time_of_day1));


int f = mktime(&str_time);
printf("\n mktime: %d \n", f);

int g = mktime(&str_time1);
printf("\n mktime: %d \n", g);

return 0;
}


**********************************************************************
output:
**********************************************************************

sh-4.2$ main                                                                                                                                                                                       

Thu Jul  5 10:03:05 2012                                                                                                                                                                           

Wed Feb  1 01:01:01 2017                                                                                                                                                                           

                                                                                                                                                                                                   

 mktime: 1341482585                                                                                                                                                                                

                                                                                                                                                                                                   

 mktime: 1485910861