How can I input data to array and print them through function?

Question

I am trying to input data to an array and then print them by using a function but I am not sure how to organize the code.

#include <iostream>
using namespace std;

void showGrade(double grade[], int size);

int main()
{
    double grade[];
    int size;

    for (int i = 0; i < size; i++) 
    {
        cout << "Please enter the number of grade" << endl;
        cin >> size;
    }

    showGrade(grade, size);
    return 0;
}

void showGrade(double grade[], int size)    //How many grade we have
{
    for (int counter = 0; counter < size; counter++) 
    {
        cout << "Please enter your grades: " << endl;
        cin >> grade[counter];
        cout << "Here are your grades: " << endl;
    }
}

I Expect to see how many grades I input and then show them.

UPDATE 8/28/19

I figured out how to do it in main function successfully. But what I really want is to put them in a seperate function. My new codes have error at the function call which is type name is not allowed and expected a ')'. How do I make it work?

#include <iostream>
using namespace std;

void showGrades(double ar[], int size);

int main()
{
    double ar[20];
    int size;

    showGrades(double ar[size], int size);

    system("pause");
    return 0;
}

void showGrades(double ar[], int size) {
    cout << "Please enter the number of grade "; // array size
    cin >> size;
    cout << "Please enter your grades " << endl;
    for (int i = 0; i < size; i++) {
        cin >> ar[i];
    }

    cout << "The grades you entered are: " << endl;

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

int size; for (int i = 0; i < size; i++) { - That'll never work. size is uninitialized. — Jesper Juhl
– Jesper Juhl, Commented Aug 22, 2019 at 19:26
Unrelated: I would not expect a function named showGrade to take inputs fro grades. I would expect it to merely show grades. An InputGrades function should be created to handle the input task. In general, a function should do only one thing (even if that one thing is to aggregate the results of a bunch of functions that each do one thing) and be named according to the one thing it does. This allows you to build very simple and easily tested functions that serve as building blocks for a more complicated program, testing everything as you go. — user4581301
– user4581301, Commented Aug 22, 2019 at 20:10
Oh I thought I did initialize the size already. So where should I do it? in the main function? — Minh Nguyen
– Minh Nguyen, Commented Aug 23, 2019 at 2:32

JeJo · Accepted Answer · 2019-08-22 19:34:32Z

1

First of all, you need to use the standard container std::vector instead of the double grade[];, since you want a variable-length array as per user input.
Secondly, you are using un-initialized size variable in
```
for (int i = 0; i < size; i++) 
```
hence it will be initialized with a garbage value. There you need no for-loop

A good starting would be:

#include <iostream>
#include <vector>    // std::vector
void showGrade(std::vector<double>& grade)
//            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -> pass the vector by ref, as the grades should be inseted to the it
{
    // the logic
}

int main()
{
    int size;
    std::cout << "Please enter the number of grade" << endl;
    std::cin >> size;

    std::vector<double> grade;
    grade.reserve(size); // reserve memory for unwanted re-allocations

    showGrade(grade);
    return 0;
}

I leave it to you to complete, after reading about the std::vector more.

Also, do not practice with using namespace std;. Read more: Why is "using namespace std;" considered bad practice?

edited Aug 22, 2019 at 19:34

answered Aug 22, 2019 at 19:15

JeJo

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6 Comments

Minh Nguyen Over a year ago

Thanks for your suggestion, I'll read more how to use vector cause I don't about it.

JeJo Over a year ago

@MinhNguyen You are welcome: might be interesting to have a short read on the followings:How to add an element in Vector using vector::push_back and How to print out the contents of a vector?

Minh Nguyen Over a year ago

I figured out how to do it in main function successfully. But what I really want is to put them in a separate function. My new codes have error at the function call which is type name is not allowed and expected a ')'. How do I make it work?

Minh Nguyen Over a year ago

I updated below the original code. Just scroll down a little bit.

Minh Nguyen Over a year ago

That's ok, I found out the way by adding & to the function prototype and function declaration. Thank you.

|

Oblivion · Accepted Answer · 2019-08-22 19:10:59Z

1

this is not a valid C++ code:

double grade[];

You can use std::vector:

std::vector<double> grade;

To insert a grade to the vector you can use grade.push_back(someGrade);

answered Aug 22, 2019 at 19:10

Oblivion

7,3922 gold badges16 silver badges34 bronze badges

2 Comments

user10957435 Over a year ago

Not sure this answers the question. Should probably be a comment instead.

Minh Nguyen Over a year ago

Thank you, I don't really know how to use vector yet but I'll read more about it.

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