Read the grade of students by Array C++

Question

This simple program to read the grade of students. I want to take how many students the user want to enter, but when I'm writing int g[size];it will be compilation error! I wonder how can I write it correct?

#include <iostream> 
using namespace std;

    int main()
    {
        int x;
        cout << "Enter how many student ..?  ";
        cin >> x;
         const int size = x;
        int g[size];
        cout << "enter " << size << "your ";
        for (int i = 0; i < size; i++){
            cin >> g[i];
        }
        for (int i = 0; i < size; i++){
            cout << "student" << i + 1 << "grade is : " << g[i] << endl;
        }

   system("pause");
    return 0 ;
}

"but when I'm writing int g[size];it doesn't work!" What exactly do you mean by *it doesn't work*? Won't compile? Crashes? Doesn't do what you expected? Be specific. — Borgleader, Dec 06 '14 at 20:37
What do you mean by "it doesn't work"? Is there an error? If the result is different than what you want, in which way? Please give us more details. — Sentry, Dec 06 '14 at 20:38
Crashes ! If I write const int size=4 (value) it will be work but I want the user to enter the size — Khan, Dec 06 '14 at 20:40
@David How do you do this? I took a copy but it something wrong! — Khan, Dec 06 '14 at 20:45
That's an exact copy paste. Try cleaning and rebuilding your project. — David, Dec 06 '14 at 20:49
http://stackoverflow.com/questions/7812566/why-no-variable-size-array-in-stack/7812587#7812587 — Thomas Padron-McCarthy, Dec 06 '14 at 21:04
@ThomasPadron-McCarthy thanks, that's mean I can not write it in c++ ! — Khan, Dec 06 '14 at 21:13

score 1 · Accepted Answer · answered Dec 06 '14 at 21:15

The line int g[size]; causes a compile error because size is not known at compile time (but obviously at runtime). So you need to allocate memory for the array at runtime.

int *g = new int[size]; // instead of int g[size];

This stores a pointer to the first element of the array in g. Now the compiler can no longer track the lifetime of the array and delete it for you when it isn't needed anymore so you need to do this yourself as well.

delete[] g; // this frees the memory again
system("pause");

As a side note: Your program is valid C++14 which is not yet (fully) supported by Microsoft's Visual C++ compiler but other compilers like clang and g++ already support it.

Thank you :) I wonder what are the different between c++ 11 and c++14 ...? — Khan, Dec 06 '14 at 21:23

Read the grade of students by Array C++

1 Answers1