srand

functions

<cstdlib>

void srand ( unsigned int seed );

Initialize random number generator

The pseudo-random number generator is initialized using the argument passed as seed.

For every different seed value used in a call to srand, the pseudo-random number generator can be expected to generate a different succession of results in the subsequent calls torand.
Two different initializations with the same seed, instructs the pseudo-random generator to generate the same succession of results for the subsequent calls torand in both cases.

If seed is set to 1, the generator is reinitialized to its initial value and produces the same values as before any call torand or srand.

In order to generate random-like numbers, srand is usually initialized to some distinctive value, like those related with the execution time. For example, the value returned by the functiontime (declared in header <ctime>) is different each second, which is distinctive enough for most randoming needs.

Parameters

seed

An integer value to be used as seed by the pseudo-random number generator algorithm.

Return Value

(none)

Example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

/* srand example */#include <stdio.h>#include <stdlib.h>#include <time.h>int main (){  printf ("First number: %d\n", rand() % 100);  srand ( time(NULL) );  printf ("Random number: %d\n", rand() % 100);  srand ( 1 );  printf ("Again the first number: %d\n", rand() %100);  return 0;}

Output:

First number: 41Random number: 13Again the first number: 41

See also

randGenerate random number (function)