随机产生浮点数？？？应该很容易了吧？？？

[zjg751206]

float lo;
lo= (float)rand()*120.0;
float la = (float)rand()*50;
为什么产生不了。每个都是一样的。如何产生不一样的浮点数

[dzmsoft]

在 rand() 函数程序运行之前调用 srand( (unsigned)time( NULL ) );

[afc]

/* A C-program for MT19937: Real number version */
/* genrand() generates one pseudorandom real number (double) */
/* which is uniformly distributed on [0,1]-interval, for each */
/* call. sgenrand(seed) set initial values to the working area */
/* of 624 words. Before genrand(), sgenrand(seed) must be */
/* called once. (seed is any 32-bit integer except for 0). */
/* Integer generator is obtained by modifying two lines. */
/* Coded by Takuji Nishimura, considering the suggestions by */
/* Topher Cooper and Marc Rieffel in July-Aug. 1997. */

/* This library is free software; you can redistribute it and/or */
/* modify it under the terms of the GNU Library General Public */
/* License as published by the Free Software Foundation; either */
/* version 2 of the License, or (at your option) any later */
/* version. */
/* This library is distributed in the hope that it will be useful, */
/* but WITHOUT ANY WARRANTY; without even the implied warranty of */
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. */
/* See the GNU Library General Public License for more details. */
/* You should have received a copy of the GNU Library General */
/* Public License along with this library; if not, write to the */
/* Free Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA */
/* 02111-1307 USA */

/* Copyright (C) 1997 Makoto Matsumoto and Takuji Nishimura. */
/* Any feedback is very welcome. For any question, comments, */
/* see http://www.math.keio.ac.jp/matumoto/emt.html or email */
/* [e-mail] */

#include<stdio.h>

/* Period parameters */
#define N 624
#define M 397
#define MATRIX_A 0x9908b0df /* constant vector a */
#define UPPER_MASK 0x80000000 /* most significant w-r bits */
#define LOWER_MASK 0x7fffffff /* least significant r bits */

/* Tempering parameters */
#define TEMPERING_MASK_B 0x9d2c5680
#define TEMPERING_MASK_C 0xefc60000
#define TEMPERING_SHIFT_U(y) (y >> 11)
#define TEMPERING_SHIFT_S(y) (y << 7)
#define TEMPERING_SHIFT_T(y) (y << 15)
#define TEMPERING_SHIFT_L(y) (y >> 18)

static unsigned long mt[N]; /* the array for the state vector */
static int mti=N+1; /* mti==N+1 means mt[N] is not initialized */

/* initializing the array with a NONZERO seed */
void
sgenrand(seed)
unsigned long seed;
{
/* setting initial seeds to mt[N] using */
/* the generator Line 25 of Table 1 in */
/* [KNUTH 1981, The Art of Computer Programming */
/* Vol. 2 (2nd Ed.), pp102] */
mt[0]= seed & 0xffffffff;
for (mti=1; mti<N; mti++)
mt[mti] = (69069 * mt[mti-1]) & 0xffffffff;
}

double /* generating reals */
/* unsigned long */ /* for integer generation */
genrand()
{
unsigned long y;
static unsigned long mag01[2]={0x0, MATRIX_A};
/* mag01[x] = x * MATRIX_A for x=0,1 */

if (mti >= N) { /* generate N words at one time */
int kk;

if (mti == N+1) /* if sgenrand() has not been called, */
sgenrand(4357); /* a default initial seed is used */

for (kk=0;kk<N-M;kk++) {
y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
mt[kk] = mt[kk+M] ^ (y >> 1) ^ mag01[y & 0x1];
}
for (;kk<N-1;kk++) {
y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
mt[kk] = mt[kk+(M-N)] ^ (y >> 1) ^ mag01[y & 0x1];
}
y = (mt[N-1]&UPPER_MASK)|(mt[0]&LOWER_MASK);
mt[N-1] = mt[M-1] ^ (y >> 1) ^ mag01[y & 0x1];

mti = 0;
}

y = mt[mti++];
y ^= TEMPERING_SHIFT_U(y);
y ^= TEMPERING_SHIFT_S(y) & TEMPERING_MASK_B;
y ^= TEMPERING_SHIFT_T(y) & TEMPERING_MASK_C;
y ^= TEMPERING_SHIFT_L(y);

return ( (double)y / (unsigned long)0xffffffff ); /* reals */
/* return y; */ /* for integer generation */
}

/* this main() outputs first 1000 generated numbers */
main()
{
int j;

sgenrand(4357); /* any nonzero integer can be used as a seed */
for (j=0; j<1000; j++) {
printf("%5f ", genrand());
if (j%8==7) printf("\n");
}
printf("\n");
}

[zjg751206]

谢谢。关键问题是在
ontimer()中不能产生随机数。我搞不懂这么个简单问题

[afc]

ontimer()一样可以产生随机数，关键是要在第一次使用rand函数之前调用srand