Storing numbers in an array then calling from a function

[spareforme]

Hi, fairly new to C programming. I have been asked to generate a list of numbers and store the prime ones in an array so that they can be then later printed out in columns.

My generateprime function is working fine and i can list all the prime numbers i need but I need to know how to add the prime numbers found to an array,

eg

 
 
    do {
 
        if the value is prime
        {
            printf(output the found prime to screen);
            move on to test next numbers along
        // i believe i need to add the found prime to the array here
                               // but i will be using a function to pass the array through 
                               // and im not sure what to do.
 
        }
        else
        {
            move on to test next numbers along
        }
 
    }while (the counter is less than requested amount);
    //CALL Show prime function array
}  

I am making a function which the program can call to list the numbers found in columns on a screen.

sort of like this

 
void showprimes(int array[]) 
{
 printf(every 5 primes found for example a new line begins)
} 

Im really just getting very confused. If someone could help me understand how to store the found primes into an array and then call them from a function I would be very grateful.

[Banfa]

One of the problems with storing something like primes in an array is that you have to know how many entries you will need when you create the array.

However you can get round this by allocating memory (function: malloc) and using a pointer to hold the address, you can then use this pointer as an array name (simply speaking). If you runout of space in your allocated array you can simply allocate more memory (function: realloc).

The all you need to do is have a variable that gives the next array index to write to, this would be initialised to 0, everytime you find a prime number you execute the following pseudo code

if (nextIndex == maxIndex)
{
    reallocate array
    recalculate maxIndex
}
 
array[nextIndex] = newPrimaryNumber;
nextIndex++;
 

[spareforme]

Thanks for the reply. I dont know much about pointers. Im attempting to store 1000 prime numbers found in the array and then call it later using a function to display these 1000 in columns.

[Banfa]

Pointers aren't that hard but if you have a defined limit (1000) then an array will do fine

the pseudo code I posted modifies to

if (nextIndex < 1000)
{
    array[nextIndex] = newPrimaryNumber;
    nextIndex++;
}
 

printing is simple, by this time of course nextIndex contains the number of primes in the array (should be 1000)

for(temp = 0; temp<nextIndex; temp++)
{
    printf("%d ", array[temp]);
}
 

I will leave it to you to work out how in insert the new lines but you will probably want to make use of the % operator.

[spareforme]

Thank you very much. I will look into it.