CODEWITHSUNDEEP
c++arrayspointers
Alphas77
Alphas77

Reputation: 1

Arrays and Pointers +Errors

Here is the assignment:

Your goal is to write a program that displays a series of whole numbers from input in reverse order. Your program will prompt the user for the number of values in this list, which it will use as the size for a dynamic array declared after this prompt.

The array size is unknown, the value is the pointer, and the sub has to be assigned before the loop.

Here are the steps:

  1. Declare variables, but don't "allocate the memory the memory for the pointer yet". Do this after prompting the user to enter the values.
  2. Prompt user to enter the numbers of values to be listed. (There has to be a message for the user in case they enter a negative number). Then use the keyword new for the pointer.
  3. Prompt the user to enter the values
  4. Display the values in reverse.
  5. Use the keyword delete for the dynamic array.

While I'm trying to run the program, the error was:

error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
for(int sub = 0; sub < size; size--)
--------------------------------------^
error: lvalue required as decrement operand
for (int sub = 0; sub > size; size--)
------------------------------------------------------^

Also, I am not sure what the keyword new does.

#include <iostream>
using namespace std;

int main()
{
    int size, array;

    cout << "How many values would you like to enter? ";
    cin >> array;
    
    
    int value;
    int *array = new int[size];
    
    if (size > 0)
    {
        for (int sub = 0; sub < size; size++)
        {
            cout << "Enter value #" << size << ": ";
            cin >> value;
        }
        while (size > 0);
    }
    
    else
    {
        while (size < 0)
        {
            cout << "Size must be positive." << endl;
            cout << "How many values would you like to enter? ";
            cin >> size;
        }
    }
    
    cout << "Here are the values you entered in reverse order: \n";
    
    for (int sub = size - 1; sub >= 0; size--) 
    {
        cout << "Value #" << size << " :" << value << endl;
    }
    
    delete[] array;

    return 0;
}

PS: I know size is supposed to be unknown, but I've encountered another error saying

storage size of ‘size’ isn’t known

So, I add numbers to avoid that error.

Edit:So I changed the code thanks to @MikeCAT, but this error said terminate called after throwing an instance of 'std::bad_array_new_length what(): std::bad_array_new_length. This was because I enter a negative number for the size, which was supposed to happen for the if statement. Also, I need the size to start at 1 after the user enters how many values they want to enter, but the size always starts at the number that was entered.

Upvotes: 0

Views: 116

Answers (1)

MikeCAT
MikeCAT

Reputation: 75062

As the assignment says, you should

  1. Read a value
  2. Allocate a dynamic array using the value read as its size
  3. Read the numbers for the array
#include <iostream>

int main(void) {
    // read a number (size of a dynamic array)
    int numElements;
    std::cin >> numElements;

    // allocate a dynamic array
    int *array = new int[numElements];

    // read values for the dynamic array
    for (int i = 0; i < numElements; i++) {
        std::cin >> array[i];
    }

    // print the values in reversed order
    for (int i = numElements - 1; i >= 0; i--) {
        std::cout << array[i] << '\n';
    }

    // de-allocate the array
    delete[] array;

    // exit normally
    return 0;
}

Error handling and non-essensial messages are omitted. Try adding them.

Upvotes: 1

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