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

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;
}
}

Answer 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?

Answer 2

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);