the value of variable cannot be used as a constant to declare an array ?? ERROR

Question

It shows error saying the variable cant be used to declare the array I don't know why, am I missing some header files?

#include<iostream>
#include<conio.h>
#include<vector>
#include<stdio.h>
#include<algorithm>
#include<math.h>
#include<queue>
#include<stack>
#include<map>
#include<unordered_map>
#include<set> 

int main()
{
    int v=4;
    bool visited[v]; //part of the code... 
}