怎样用rand函数？

[kaishuinanhai]

怎样用rand（）产生N个随机整数（20000以上）；

[龙哥依旧]

// crt_rand.c
// This program seeds the random-number generator
// with the time, then exercises the rand function.
//

#include <stdlib.h>
#include <stdio.h>
#include <time.h>

void SimpleRandDemo( int n )
{
   // Print n random numbers.
   int i;
   for( i = 0; i < n; i++ )
      printf( "  %6d\n", rand() );
}

void RangedRandDemo( int range_min, int range_max, int n )
{
   // Generate random numbers in the half-closed interval
   // [range_min, range_max). In other words,
   // range_min <= random number < range_max
   int i;
   for ( i = 0; i < n; i++ )
   {
      int u = (double)rand() / (RAND_MAX + 1) * (range_max - range_min)
            + range_min;
      printf( "  %6d\n", u);
   }
}

int main( void )
{
   // Seed the random-number generator with the current time so that
   // the numbers will be different every time we run.
   srand( (unsigned)time( NULL ) );

   SimpleRandDemo( 10 );
   printf("\n");
   RangedRandDemo( -100, 100, 10 );
}

[十八道胡同]

先设置时间种子 然后rand()

[就想叫yoko]

百度百科 rand srand

[anhuihulei]

#include <time.h>

srand((int )time(NULL));
int nNum = rand() + 20000;//20000到52767的随机数
rand（）范围（0~32767）

[kaishuinanhai]

[Quote=引用 4 楼 anhuihulei 的回复:]
#include <time.h>

srand((int )time(NULL));
int nNum = rand() + 20000;//20000到52767的随机数
rand（）范围（0~32767）
[/Quote]怎样体现出N个呢

[matrixcl]

[Quote=引用 5 楼 kaishuinanhai 的回复:]

引用 4 楼 anhuihulei 的回复:
#include <time.h>

srand((int )time(NULL));
int nNum = rand() + 20000;//20000到52767的随机数
rand（）范围（0~32767）
怎样体现出N个呢
[/Quote]

srand((int )time(NULL));

for (int i=0; i<100; i++)
{
    int nNum = rand() + 20000;//20000到52767的随机数
}

[kaishuinanhai]

[Quote=引用 6 楼 matrixcl 的回复:]
引用 5 楼 kaishuinanhai 的回复:

引用 4 楼 anhuihulei 的回复:
#include <time.h>

srand((int )time(NULL));
int nNum = rand() + 20000;//20000到52767的随机数
rand（）范围（0~32767）
怎样体现出N个呢


C/C++ code


srand(……
[/Quote]这不是取一百个数了，这个N也太不合理了，但是谢谢你咯，还是用cin>>N;来确定吧！

[一根烂笔头]

#include <iostream>
#include <ctime>
using namespace std;

int main()
{
    srand((int )time(NULL));
    for (int i=0; i<1000; i++)
    {
        int nNum = 20000+rand() % (RAND_MAX-20000);//20000到52767的随机数
    }
}

[一根烂笔头]

int rand ( void );

Generate random number
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 <cstdlib>. 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.

Example
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/* rand example: guess the number */
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

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 (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;
}



Output:


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
Congratulations!



In this example, the random seed is initialized to a value representing the second in which the program is executed (time is defined in the header <ctime>). This way to initialize the seed is generally a good enough option for most randoming needs.

See also

[cnlm2]

int num = rand()%20000 + 20000;

这个就可以产生20000以上了

[hawl2004]

srand((unsigned)time(NULL));

[一根烂笔头]

int rand ( void );

Generate random number
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 <cstdlib>. 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.

Example
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/* rand example: guess the number */
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

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 (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;
}



Output:


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
Congratulations!



In this example, the random seed is initialized to a value representing the second in which the program is executed (time is defined in the header <ctime>). This way to initialize the seed is generally a good enough option for most randoming needs.

See also

[Eric_SEU]

#include <iostream>
using namespace std;
#include <ctime>
#include <iomanip>

int main()
{
srand(time(0));
int a[100];
for(int i=0 ;i <100 ; i++)
{
a[i]= rand();
}
return 0;
}//这是一个产生随机数的例子 ，楼主做参考吧