Error in array declaration: Expression must have a constant value

Question

I declared a global struct with the following structure:

typedef struct {
    int value;
    int index;
}element;

I have a program with k sorted queues, and I put in a heapSort(I am using an array) the minimum from each one. I use the index value in struct to track the element that I want to pop out of the heap. Now, I want to test the program for different number of queues, so I did this:

for (int i = 10;i <= 50;i += 10) {
    const int k = i;
    element a[k];
}

But I get an error:

Expression must have a constant value

Is there any way I can "trick" that?

Standard C++ does not have variable length arrays (C does). Use std::vector instead. — Richard Critten
– Richard Critten, Commented Apr 3, 2017 at 21:21
std::vector<element> a(i); and throw out k entirely. And fyi, if allowed by whatever purpose this is for, the heap operations in <algorithm> will come in very handy and save you a ton of code. If this is for a priority queue, the std::priority_queue adapter can save you even more effort. — WhozCraig
– WhozCraig, Commented Apr 3, 2017 at 21:22

andria_girl · Accepted Answer · 2017-04-03 22:00:03Z

1

You declared an array, an array's size cannot be changed. To solve this issue it would be in your best interest to use a vector.

Try this:

#include <vector>
vector <element> a(50);

To pop elements out of the vector try this:

a.erase(a.begin()+index_from_zero);

edited Apr 3, 2017 at 22:00

answered Apr 3, 2017 at 21:30

andria_girl

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