For the prime numbers array:
Do some for- / while-loop and check every number above your passed "somenumber" if it's a prime number. If it's a prime number, add it to the array.
This is how it could look (not sure if there are any syntax errors)
PHP Code:
for (int i = somenumber; i < 500; i++) {
if (primenumber) { // insert your prime number check here
*higharray++ = i;
}
}
If you want to do this for the first 10 prime numbers, take a look at a while-loop where you count up an integer every time you've found a prime number.
To get the average:
int average = 0;
int counter = 0;
while (*higharray++ != null) {
average+= *higharray;
++counter;
}
average = (int)(average / counter);
-> just add every prime number you've found and divide it by the total amount of found prime numbers. If there are only 10 prime numbers, you don't need the counter variable, just divide by 10.