您应该使用该arc4random_uniform()功能。它使用高级算法来rand. 你甚至不需要设置种子。

#include <stdlib.h>
// ...
// ...
int r = arc4random_uniform(74);

arc4random手册页：

NAME
     arc4random, arc4random_stir, arc4random_addrandom -- arc4 random

number generator

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdlib.h>

     u_int32_t
     arc4random(void);

     void
     arc4random_stir(void);

     void
     arc4random_addrandom(unsigned char *dat, int datlen);

DESCRIPTION
     The arc4random() function uses the key stream generator employed by

the arc4 cipher, which uses 88 8
bit S-Boxes. The S-Boxes can be in about (21700) states. The
arc4random() function returns pseudo-
random numbers in the range of 0 to (2*32)-1, and therefore has
twice the range of rand(3) and
random(3).

     The arc4random_stir() function reads data from /dev/urandom and

uses it to permute the S-Boxes via
arc4random_addrandom().

     There is no need to call arc4random_stir() before using

arc4random(), since arc4random() automatically
initializes itself.

EXAMPLES
     The following produces a drop-in replacement for the traditional

rand() and random() functions using
arc4random():

           #define foo4random() (arc4random() % ((unsigned)RAND_MAX +

1))