Function that fills an Array with random integers(including negative)-CodePudding

I want to fill an array with random integers from -10 to 10. My function looks like this:

int array(int a[], int n, int min, int max){

for(int i=0;i<n;i  ){
    a[i]=(rand()%min);
    printf("%d ", a[i] );
}

In main I have declared "min" to -10. But it does not really work, it still prints between 0 - 9. I have tried with 1 after min, then i get 10, but still no negative integers.

CodePudding user response：

Get a random number properly:

int random( int min, int max )
{
  int N = max - min   1;
  int K = RAND_MAX - (RAND_MAX % N);
  int n;
  do n = rand(); while (n >= K);
  return (n % N)   min;
}

This function cannot give you random values in ranges with magnitude greater than RAND_MAX, and RAND_MAX is often fairly small (32,767). If you need a greater range, let us know.

Thereafter, apply the function to each element of your array:

void randomize_array( int a[], int n, int min, int max )
{
  while (n--) a[n] = random( min, max );
}

Keep separate operations separate. Randomizing an array has nothing to do with printing it. Print separately:

void print_array( int a[], int n )
{
  if (!n) return;
  printf( "%d", a[0] );
  for (int i = 1;  i < n;  i  )
    printf( " %d", a[i] );
  printf( "\n" );
}

Putting it all together:

#define sizeof_array(A) (sizeof((A)) / sizeof((A)[0]))

int a[20];

randomize_array( a, sizeof_array(a), -10, 10 );
print_array( a, sizeof_array(a) );

CodePudding user response：

The number of possible number is max - min 1, so that's what you want to mod by, giving you a number from 0 to max - min. Then you add min to that to give you a number from min to max.

a[i]=(rand() % (max-min 1)   min );

CodePudding user response：

The % (modulus) operator divides two integer types and returns the remainder, which is always positive or zero. This is why no negative numbers are getting inserted. Try:

a[i] = (rand()!) - 10;

Also, make sure to return a value from your function. Perhaps int * makes more sense, if you're returning the array you generated.