c++ references array - c++

Question

I wounder how i can make this code work?
#include <iostream>
using namespace std;
void writeTable(int (&tab)[],int x){
for(int i=0;i<x;i++){
cout << "Enter value " << i+1 <<endl;
cin >> tab[i] ;
}
}
int main(void){
int howMany;
cout << "How many elemets" << endl;
cin >> howMany;
int table[howMany];
int (&ref)[howMany]=table;
writeTable(ref,howMany);
return 0;
}
And here are the errors that I have:
|4|error: parameter ‘tab’ includes reference to array of unknown bound ‘int []’|
|18|error: invalid initialization of reference of type ‘int (&)[]’ from expression of type ‘int [(((unsigned int)(((int)howMany) + -0x00000000000000001)) + 1)]’|
|4|error: in passing argument 1 of ‘void writeTable(int (&)[], int)’|
Thanks for help

Answer 1

If you are intending to pass the size of the array, then remove the reference
void f(int a[])
is equivalent to
void f(int* a)
so no copying will be done, if that is the concern.
If you want to take an array by reference, then you MUST specify the dimension. e.g.
void f(int (&a)[10])
Naturally, the best of the two is the third solution, which is to use std::vector's and pass them by reference, reference to const or by value if needed. HTH

Answer 2

Here is a slightly more C++ style of doing it:
#include <iostream>
#include <vector>
void writeTable(std::vector<int> &tab)
{
int val;
for (unsigned int i=0; i<tab.size(); i++)
{
std::cout << "Enter value " << i+1 << std::endl;
if (std::cin >> val)
{
tab[i] = val;
}
}
}
int main()
{
int howMany;
std::cout << "How many elements?" << std::endl;
std::cin >> howMany;
std::vector<int> table(howMany);
writeTable(table);
return 0;
}

Answer 3

You need not specify the dimension of the array if you make writeTable a function template.
template <typename T,size_t N>
void writeTable(T (&tab)[N]) //Template argument deduction
{
for(int i=0 ; i<N ; i++){
// code ....
}
}
.
int table[howMany]; // C++ doesn't have Variable Length Arrays. `howMany` must be a constant
writeTable(table); // type and size of `table` is automatically deduced

Answer 4

Following Amardeep's answer, here is a C++11 way to do it:
#include <iostream>
#include <vector>
void writeTable(std::vector<int> &tab)
{
int val;
for (auto& cell : tab)
{
std::cout << "Enter value " << i+1 << std::endl;
if (std::cin >> val)
{
cell = val;
}
}
}
int main()
{
int howMany;
std::cout << "How many elements?" << std::endl;
std::cin >> howMany;
std::vector<int> table(howMany);
writeTable(table);
return 0;
}
Note the range-based for used in writeTable.

Answer 5

Arrays of references are illegal, if that is what you are trying to do. It's not 100% clear to me from the title.