how can i delete dynamic array created in a function

Question

I have to write a program (not using vector, nor using structures nor OOP) which calculates the sum and the product of two polynomials. Here is my code:

//Task 4.19 & 4.20
#include <iostream>
#include <cmath>
double* definePoly(char& symbol, char& coef, int& k)
{
    std::cout << "deg(" << symbol << "(x)) = ";
    std::cin >> k;
    symbol++;
    double* a = new double[k];
    for (int i = k; i >= 0; i--)
    {
        std::cout << coef << "_{" << i << "} = ";
        std::cin >> a[i];
    }
    coef++;
    return a;
}
void printPoly(int n, double* P, char& symbol)
{
    symbol--;
    std::cout << symbol << "(x)=";
    for (int i = n; i >= 0; i--)
    {
        if (P[i] != 0)
        {
            if (P[i] > 0)
            {
                std::cout << '+';
            }
            std::cout.setf(std::ios::fixed);
            std::cout.precision(2);
            std::cout << P[i] << ".x^{" << i << "}";
        }
    }
    std::cout << "\n";
    symbol++;
}
double* sumPoly(double* a, int n, double* b, int m, char& symbol)
{ // Task 4.19
    symbol++;
    double* c = new double[(n + m + abs(n - m)) / 2];
    if (n > m)
    {
        for (int i = 0; i <= m; i++) c[i] = a[i] + b[i];
        for (int i = m + 1; i <= n; i++) c[i] = a[i];
    }
    else if (n < m)
    {
        for (int i = 0; i <= n; i++) c[i] = a[i] + b[i];
        for (int i = n + 1; i <= m; i++) c[i] = b[i];
    }
    else for (int i = 0; i <= n; i++)c[i] = a[i] + b[i];
    return c;
}
double* prodPoly(double* a, int n, double* b, int m, char& symbol)
{ // Task 4.20
    symbol++;
    double* d = new double[n + m];
    for (int p = 0; p <= n + m; p++)
    {
        d[p] = 0;
        for (int i = 0; i <= n; i++)
            for (int j = 0; j <= m; j++)
                if (i + j == p) d[p] = d[p] + a[i] * b[j];
    }
    return d;
}
int main()
{
    int n, m;
    char symbol('P'), coef('a');

    double* firstPoly = definePoly(symbol, coef, n);
    printPoly(n, firstPoly, symbol);

    double* secondPoly = definePoly(symbol, coef, m);
    printPoly(m, secondPoly, symbol);

    double* sum = sumPoly(firstPoly, n, secondPoly, m, symbol);
    std::cout << "Sum:\n";
    printPoly((n + m + abs(n - m)) / 2, sum, symbol);

    double* prod = prodPoly(firstPoly, n, secondPoly, m, symbol);
    std::cout << "Product:\n";
    printPoly(n + m, prod, symbol);

    /*delete[] firstPoly;
    delete[] secondPoly;
    delete[] sum;
    delete[] prod;*/

    return 0;
}

It works perfectly, but when I uncomment the deleting, visual studio tells me that there is an error, otherwise there are leaks.

How can I delete/release the memory in order to solve this problem?

What are the "error" you get if you try to delete[] the arrays? Are you sure you don't go out of bounds of the allocated memory? The definePoly function definitely go out of bounds. — Some programmer dude
– Some programmer dude, Commented Jul 29, 2019 at 11:28
"visual studio tells me that there is an error" what error? please include it in the question — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Jul 29, 2019 at 11:28
What happens if you uncomment the deletes? This should work on the first glance. Also, necessary comment: use std::vector instead of manual memory management. — Yksisarvinen
– Yksisarvinen, Commented Jul 29, 2019 at 11:28
If the delete of a heap allocated pointer isn't working it tells you that your program has a bug, not that you were doing the delete wrongly. New programmers often think bugs are caused by deletes, but almost always something has gone wrong some time before the delete and that is the real bug. — john
– john, Commented Jul 29, 2019 at 11:44

eerorika · Accepted Answer · 2019-07-29 11:41:49Z

7

double* a = new double[k];
for (int i = k;
    std::cin >> a[i];

The index of the last element of an array of k elements is k - 1 You access the arrays out of bounds in all your loops (this is just one of them) . The behaviour of the program is undefined.

how can i delete dynamic array created in a function

Just like you would delete a dynamic array created outside of a function, and just like you've attempted to delete it:

delete[] firstPoly; // etc

But you must make sure that your program doesn't corrupt its own memory with undefined behaviour.

edited Jul 29, 2019 at 11:41

answered Jul 29, 2019 at 11:36

eerorika

240k13 gold badges212 silver badges354 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

CrazyMan Over a year ago

Is it considered okay to use new and delete in different scopes, so to say? The new is called in one function but delete is called in another function.

Collectives™ on Stack Overflow

how can i delete dynamic array created in a function

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related