rand

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06/05/2017

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Generates a pseudorandom number. A more secure version of this function is available, see rand_s.

Syntax

int rand( void );

Return Value

rand returns a pseudorandom number, as described above. There is no error return.

Remarks

The rand function returns a pseudorandom integer in the range 0 to RAND_MAX (32767). Use the srand function to seed the pseudorandom-number generator before calling rand.

Requirements

Routine	Required header
`rand`	<stdlib.h>

For additional compatibility information, see Compatibility in the Introduction.

Example

// 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 );  
}

.NET Framework Equivalent

System::Random Class

共用方式為