Generazione numero casuali

[LukA4e]

Ciao a tutti mi potete dire come faccio a scrivere un programma in C che in una variabile c metta un numero casuale d 1 a 6 e me lo faccia vedere????? Ciao e grazie a tutti!

[gurutech]

pagina man di rand(3):
SYNOPSIS

#include <stdlib.h>
int rand(void);
void srand(unsigned int seed);

DESCRIPTION
The rand() function returns a pseudo-random integer between 0 and RAND_MAX.

The srand() function sets its argument as the seed for a new sequence of pseudo-random integers to be returned by rand (). These sequences are repeatable by calling srand() with the same seed value.

If no seed value is provided, the rand() function is automatically seeded with a value of 1.

RETURN VALUE The rand() function returns a value between 0 and RAND_MAX. The srand() returns no value.

NOTES The versions of rand() and srand() in the Linux C Library use the same random number generator as random() and srandom(), so the lower-order bits should be as random as the higher-order bits. However, on older rand() implementations, the lower-order bits are much less random than the higher-order bits.

In Numerical Recipes in C: The Art of Scientific Computing (William H. Press, Brian P. Flannery, Saul A. Teukolsky, William T. Vetterling; New York: Cambridge University Press, 1992 (2nd ed., p. 277)), the following comments are made:


"If you want to generate a random integer between 1 and 10, you should always do it by using high-order bits, as in

j=1+(int) (10.0*rand()/(RAND_MAX+1.0));

and never by anything resembling

j=1+(rand() % 10);

(which uses lower-order bits)."

Random-number generation is a complex topic. The Numerical Recipes in C book (see reference above) provides an excellent discussion of practical random-number generation issues in Chapter 7 (Random Numbers).

For a more theoretical discussion which also covers many practical issues in depth, please see Chapter 3 (Random Numbers) in Donald E. Knuth's The Art of Computer Programming, volume 2 (Seminumerical Algorithms), 2nd ed.; Reading, Massachusetts: Addison-Wesley Publishing Company, 1981.

in pratica:

int dado;
srand((unsigned int) time(NULL));
dado=1+(int) (6.0*rand()/(RAND_MAX+1.0));
printf("alea iacta est: %d",dado);

notare che ho scritto 6.0 e non 6

[LukA4e]

grazie domani provo, non serve la libreria time.h?
Ciao

[gurutech]

si ti serve time.h. è scritto nella manpage di time(2)

questo è un modo semplicissimo di generare numeri casuali (e tra l'altro l'unico che so usare), ma so che se ti servono numeri veramente casuali ci sono funzioni ben più complesse. Ma d'altronde se ho capito vuoi fare un semplice dado e così va più che bene (che devi giocà a D&D ?)