C: generate array with random numbers in range (allwowing duplicates) - c

Question

I want to write a C function that gets: a seed, int n (the number of random ints to generate), and upper limit (the max allowed number).
I came so far as to have somthing like this:
// I need a function definition here
// I forgot how to allocate the int array ... somehting with 'sizeof'?
srand(time(NULL)); //seed for rand
for(i = 0; i < length; i++)
array[i] = rand()%upperLimit;
return array;
Then I probably need those header files:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

Answer 1

You need #include <time.h> for the time function.
This is simple program matching your description with comments in the code:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int *
alocate (unsigned int n)
{
return malloc (n * sizeof (int)); // allocate memory block for n numbers and return int pointer to it
}
int *
generate_block_with_random_numbers (unsigned int n, int upper_limit)
{
// function `int *generate_block_with_random_numbers(unsigned int n, int upper_limit)`
// gets a positive integer n as an argument
// reserves the n block of int variables in memory
// fills this block with random values
// returns a pointer to the beginning of the reserved block.
srand (time (NULL)); // seed generator
int *array = alocate (n); // note: array pointer always points to the beginning of the allocated memory
for (int i = 0; i < n; i++)
{
// you can index the array moving to its next element via [i]
array[i] = rand () % (upper_limit+1); //
}
return array;
}
int
main ()
{
unsigned int n = 5;
unsigned int upperL = 5;
int *block = generate_block_with_random_numbers (n, upperL);
// Display the data contained in the returned block:
for (int i = 0; i < n; i++)
{
printf ("%d\n", block[i]); // print it
}
return 0;
}
Output:
5
0
2
3
3