From the documentation: "The C library function
time_t time(time_t *seconds) returns the time since the Epoch (00:00:00 UTC, January 1, 1970), measured in seconds. If seconds is not NULL, the return value is also stored in variable seconds." If the parameter is NULL instead of a var, the function just returns the number of seconds.
This is a common technique for generating a pesudorandom seed number for srand without having to input it each time. It will produce different results for each run of the program. However, if you wanted to produce the same result each time, say for testing, you can provide a number that will be placed in argv.
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