int get_numbers(int p_prompt);
// I changed the name so that you wont get confused what is what. prompt is not forward declared here and is not available to main
// You didn't call this function with the second parameter n, since it's also not used, we need to remove it.
int prompt; // You need to declare the variable in main
for (i = 0; i <7; i++) // You are simply doing something identical 7 times. Is that intentional?
cout << get_numbers(prompt); // pass the pointer to the function
int get_numbers(int p_prompt) // I removed int n from this list because it wasn't used.
// Note that you had it in a different order than in the declaration... that's bad.
cout << "type in number";
cin >> prompt;
return 0; // note, since you're returning 0, you will cout 0 in main. Is this what you wanted?