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Random Number Generation


Random number generation


int rand ( void );
Returns a pseudo-random integral number in the range 0 to RAND_MAX. This number is generated by an algorithm that returns a sequence of apparently non-related numbers each time it is called. This algorithm uses a seed to generate the series, which should be initialized to some distinctive value using srand. RAND_MAX is a constant defined in . Its default value may vary between implementations but it is granted to be at least 32767. A typical way to generate pseudo-random numbers in a determined range using rand is to use the modulo of the returned value by the range span and add the initial value of the range: ( value % 100 ) is in the range 0 to 99 ( value % 100 + 1 ) is in the range 1 to 100 ( value % 30 + 1985 ) is in the range 1985 to 2014 Notice though that this modulo operation does not generate a truly uniformly distributed random number in the span (since in most cases lower numbers are slightly more likely), but it is generally a good approximation for short spans. Parameters (none) Return Value An integer value between 0 and RAND_MAX.

Random number example


#include < iostream·h>
/* rand example: guess the number */ #include #include #include int main () { int iSecret, iGuess; /* initialize random seed: */ srand ( time(NULL) ); /* generate secret number: */ iSecret = rand() % 10 + 1; do { printf ("Guess the number (1 to 10): "); scanf ("%d",&iGuess); if (iSecretiGuess) puts ("The secret number is higher"); } while (iSecret!=iGuess); puts ("Congratulations!"); return 0; }


Guess the number (1 to 10): 5
The secret number is higher
Guess the number (1 to 10): 8
The secret number is lower
Guess the number (1 to 10): 7