Question

For what we use time(NULL) in C to generate random values? What is the meaning of time(NULL) in this code?

 int i, zarodek;
    zarodek= time(NULL);
    srand(zarodek);
    int r = rand() % 49 + 1;
    printf("%d",r);

Answer 1

It is getting the system time (in seconds). You may optionally supply a pointer to a time_t value that will receive the time, but since the value is returned from the time function anyway, you may pass NULL instead (and the function will not attempt to assign to the null pointer).

The purpose of using time is to seed the random number generator (passing it to srand). It’s common to use the time, because it’s generally different every time your program is run.

Note, you should only seed once (not every time you call rand).