Generate random number c++

Situatie

Returns a pseudo-random integral number in the range between 0 and 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 function srand.

RAND_MAX is a constant defined in <cstdlib>

A typical way to generate trivial 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:

1
2
3

v1 = rand() % 100;         // v1 in the range 0 to 99
v2 = rand() % 100 + 1;     // v2 in the range 1 to 100
v3 = rand() % 30 + 1985;   // v3 in the range 1985-2014

Notice though that this modulo operation does not generate uniformly distributed random numbers in the span (since in most cases this operation makes lower numbers slightly more likely).

Solutie

/* rand example: guess the number */

#include <stdio.h> /* printf, scanf, puts, NULL */

#include <stdlib.h> /* srand, rand */

#include <time.h> /* time */

int main ()

{

int iSecret, iGuess;

/* initialize random seed: */

srand (time(NULL));

/* generate secret number between 1 and 10: */

iSecret = rand() % 10 + 1;

do {

printf (“Guess the number (1 to 10): “);

scanf (“%d”,&iGuess);

if (iSecret<iGuess) puts (“The secret number is lower”);

else if (iSecret>iGuess) puts (“The secret number is higher”);

} while (iSecret!=iGuess);

puts (“Congratulations!”);

return 0;

}

In this example, the random seed is initialized to a value representing the current time (calling time) to generate a different value every time the program is run.

Tip solutie

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