Store double in array C++ using Xcode

Question

I try to save declare a double array in C++ on Xcode.

double array[size];

But when I print the values,

for(int i=0; i<size; i++){
    cout<<array[i]<<"  ";
}

It's printing integers.

void display(int grade[][size_of_qz]) {

    double stAve[size_of_st];
    computeStAve(grade, stAve);

    cout << "Student      Ave         Quizes\n";
    for (int row = 0; row < size_of_st; row++) {
        cout << row + 1 << "        " << stAve[row] << "          ";
        for (int col = 0; col < size_of_qz; col++) {
            cout << grade[row][col] << "  ";
        }
        cout << endl;
    }
}

void computeStAve(int grade[][size_of_qz], double stAve[]) {
    int temp = 0;
    for (int row = 0; row < size_of_st; row++) {
        for (int col = 0; col < size_of_qz; col++) {
            temp += grade[row][col];
        }
        stAve[row] = temp / size_of_qz;
        temp = 0;
    }
}

Were you expecting the value to be printed *with* decimal points? — g-radam, Oct 22 '18 at 03:26
If you are **not** printing decimals for **any** number, then that would suggest that the value being saved in stAve[x] is wrong. std::cout prints floating point numbers with decimals by default (if its not a whole number). So the printing is not the issue. — g-radam, Oct 22 '18 at 03:38
I also suspect `stAve[row] = temp / size_of_qz;` being an integer division. — Swordfish, Oct 22 '18 at 03:39
Possible duplicate of [Integer division always zero](https://stackoverflow.com/questions/9455271/integer-division-always-zero) — phuclv, Oct 24 '18 at 05:31

score 2 · Accepted Answer · answered Oct 22 '18 at 03:35

2

Looks like this line is the cause of your problems:

stAve[row]=temp/size_of_qz;

It is the same as: double = (int / int). Your division is getting converted to an int. You need to do something like:

stAve[row]=(double)temp/size_of_qz;

answered Oct 22 '18 at 03:35

g-radam

527
1
7
20

1

Really helped. Thanks. – Sainaa Ieshua Oct 22 '18 at 04:02

score -2 · Answer 2 · answered Oct 22 '18 at 03:35

-2

If you are expecting to print a certain number of digits, start your main function with a

    std::cout << std::fixed << std::setprecision(2);

and the library to include would be iomanip.

answered Oct 22 '18 at 03:35

Drimik Roy

17
2

2

The default C++ precision is 6, changing it to 2 is not going to change the fact that he's seeing integers when expecting floats. – ChrisD Oct 22 '18 at 03:43
right, that's my bad. misinterpreted the question. Thanks for the feedback – Drimik Roy Oct 23 '18 at 04:25

Store double in array C++ using Xcode

2 Answers2