How to know size of array in c++?

Question

if i don't know how many values is to put in array by user
how can i make array
suppose
i make array
a[5]
but only 3 values is to put

Answer 1

you can use dynamic arrays or vectors
int *m, n;
cin >> n;
m = new int [n];
...
...

Answer 2

You can do what @01ejka said, or alternatively:

int a[] = {}; //Enter array
cout << sizeof(a)/sizeof(int);

Which will return the size of array.

Answer 3

You can also use a vector. The size of vectors is mutable.