# rand

Generates a pseudorandom number by using a well-known and fully-reproducible algorithm. A more programmatically secure version of this function is available; see rand_s. Numbers generated by rand are not cryptographically secure. For more cryptographically secure random number generation, use rand_s or the functions declared in the C++ Standard Library in <random>.

## Syntax

``````int rand( void );
``````

## Return Value

rand returns a pseudorandom number, as described above. There's 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.

The rand function generates a well-known sequence and is not appropriate for use as a cryptographic function. For more cryptographically secure random number generation, use rand_s or the functions declared in the C++ Standard Library in <random>. For information about what's wrong with rand and how <random> addresses these shortcomings, see this video entitled rand Considered Harmful.

By default, this function's global state is scoped to the application. To change this, see Global state in the CRT.

## Requirements

Routine Required header
rand <stdlib.h>

For additional compatibility information, see Compatibility.

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

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