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rand

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

int rand( void );

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

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.

Routine

Required header

rand

<stdlib.h>

For additional compatibility information, see Compatibility in the Introduction.

// 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 );
}
   22036
   18330
   11651
   27464
   18093
    3284
   11785
   14686
   11447
   11285

      74
      48
      27
      65
      96
      64
      -5
     -42
     -55
      66

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