Question

I am new to c++ so this doubt might look basic but I am not getting the difference between rand() and srand() and what do u mean by “seed” in srand()?
when I write srand(time(NULL)), what does it do to generate random numbers, what does time(NULL) do here? and what is it?
Thanks in advance

Answer 1

A random number generator requires a number(it is called seed) to generate random numbers . If the random number generator is given the same seed then every time it will generate the same sequence of random numbers . For example :-

If you run the program and it is generating random sequence 2,78,45,60 .
If second time you run the program you will again get the same sequence 2,78,45,60.

srand function is used to change the seed of the random number generator.By setting srand(time(NULL)) , you are setting the seed of the random number generator to the current time.By doing this every time you run the program you will get different random sequences :-

For example for the first run if you are getting 2,78,45,60 .
Next time you might get 5,3,6,80 (depending on the current time,as seed has been changed since the time has changed since the last run)

for more info refer these :-

http://www.cplusplus.com/reference/clibrary/cstdlib/rand/

http://www.cplusplus.com/reference/clibrary/cstdlib/srand/

http://www.cplusplus.com/reference/clibrary/ctime/time/