C++ arrays and functions, code not working out

Question

I'm new to programming and started out with C++ just recently, learning from a book. I have a question that asks me to write a program that has 3 separate functions that:

1. fills an array, taking input until until the array is full or when the user enters non-numeric input.
2. displays the contents of the array
3. reverses the order of the values stored in the array

The following is the code I wrote:

#include<iostream>
#include<array>
using namespace std;

int Fill_array(double*, int);
void Show_array(double*, int);
void Reverse_array(double*, int);

int main()
{
    int temp; double val[100];
    cout << "Please enter no. of values (<=100): ";
    cin >> temp;

    int num = Fill_array(val, temp);
    int x;


    cout << "Press 1 to show array & 2 to reverse array: ";
    while (cin>>x)
    {
        if (x == 1) 
            {
            Show_array(val, num);
            cout << "Press 1 to show array & 2 to reverse array: ";
            continue;
            }

        if (x == 2) 
            {
            Reverse_array(val, num); 
            cout << "Press 1 to show array & 2 to reverse array: ";
            continue; 
            }

        else
            {
            break;
            }
    } 

}



///////////////////////////////////////     function definitions

int Fill_array(double val[], int num)
{
    int x = 0;
    cout << "Enter values:";
    while (x<num && cin>>val[x])
    {
        x++;
    }
    return x;
}

void Show_array(double val[], int num)
{
    cout << "Array values: " << endl;
    for (int i = 0; i < num;i++)
    {
        cout << val[i] << endl;
    }
}

void Reverse_array(double val[], int num)
{
    for (int i = 0, j = num-1; i >= j; i++, j--)
    {
        double temp;
        temp = val[i];
        val[i] = val[j];
        val[j] = temp;
    }
}

The function Reverse_array doesn't reverse the order of the values in the array. Also, when I give non-numeric input during Fill_array, the program will cout<<"Press 1 to show array & 2 to reverse array: "; but then proceeds to skip the while loop and the program just ends.

Answer 1

To answer the part of your question dealing with getting user input once you get input that is not a number it put cin into an error state. You need to get rid of that error and clean out the buffer in order to get cin back into a known good state. You can change Fill_array() to:

int Fill_array(double val[], int num)
{
    int x = 0;
    cout << "Enter values:";
    while (x<num && cin>>val[x])
    {
        x++;
    }
    if(!cin) // cin is in error
    {
        cin.clear(); // clear error flags
        cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');  // get rid of everything in cin until you get to a newline
    }
    return x;
}

Answer 2

You have a simple logic error in your for loop in Reverse_array:

for (int i = 0, j = num-1; i >= j; i++, j--)
                            ^^^^

This should be:

for (int i = 0, j = num-1; i < j; i++, j--)
                            ^^^

Note that single-stepping through the code in your debugger would have shown you this mistake very quickly, so it's probably a good idea to start learning this and other basic debugging skills.

Note also that C++ already has support for many simple operations such as this - instead of "re-inventing the wheel" you could just use std::reverse, e.g.

void Reverse_array(double val[], int num)
{
    std::reverse(val, val + num);
}