Some test cases aren't passing - c++

Question

#include <iostream>
#include <vector>
int i=0; //points at the current stack that we are working with
int box=0; //no. of boxes held by the crane
int64_t H; //max. height of the stacks given in the que.
int main()
{
int n, value; //storing no. of stacks and creating an additional variable value to store operations
std::cin>> n >> H;
int64_t arr[n]; //storing the no. of boxes each stack has in an array
std::vector<int> arr2; //storing the operations we have to perform in a vector
for(int j=0; j<n; j++){std::cin>> arr[j];} //getting arr
while(std::cin>>value) //getting arr2
{
arr2.push_back(value);
}
for(int xy=0; xy<n; xy++){if(arr[xy]>H){return 0;}} //ensuring that all stacks have no.of boxes less than max. height
if(arr2.size()<1 || arr2.size()>10e5 || n<1 || n>10e5 || H<1 || H>10e8){return 0;} //constraints given in the que.
int k=0; //creating a variable to keep count of how many programs we have already executed
while(k<arr2.size()){
if(arr2[k] == 1){MoveLeft();}
else if(arr2[k]==2){MoveRight(n);}
else if(arr2[k]==3){PickBox(arr, i);}
else if(arr2[k]==4){Dropbox(arr, i);}
else if(arr2[k]==0){k=arr2.size();}
k++;
}
for(int j=0; j<n; j++){std::cout<< arr[j] << " ";} //printing the arr after executing the code
return 0;
}
This is a question from a past year ZCO. And the above code is what I wrote to solve the prob.
The four functions Moveleft, MoveRight, Pickbox, Dropbox have been defined in the same file but aren't shown here because I think there's no issue with them.
When I submit the code, all test cases passed except 2. I don't know what is the problem with my code. Pls help me.
I have tried my best to make the code readable. Sorry if the code looks messy.

Answer 1

With the method you're trying to define an array with a user-input length is unfortunately invalid in C++.
But fortunately, there are basically two methods use to allocate arrays dynamically.
Method 1: Using Vectors
Vector is an important part of C++. It has a lot of features (e.g. its size don't need to be defined static unlike a normal array does, can redefine array size, etc.) An example's given:
#include <iostream>
#include <vector>
int main(void) {
std::vector<int> vArray; // vector<> declaration
int size = 0;
int getInput = 0;
std::cout << "Enter an array size: ";
std::cin >> size;
for (int i = 0; i < size; i++) {
std::cout << "Enter a value: ";
std::cin >> getInput;
vArray.push_back(getInput); // inserts one+ container and data in it
}
for (int i = 0; i < vArray.size(); i++) {
// retrieving contained data...
std::cout << vArray[i] << std::endl;
}
return 0;
}
Method 2: Using 'new' Keyword with Pointed Variable
The simple use of new will help you to achieve your requirement. It's less recommended since already there's concept of vectors which actually works efficiently than arrays. Let's take a look into a simple program:
#include <iostream>
int main(void) {
int *pArray;
int size;
std::cout << "Enter an array size: ";
std::cin >> size;
pArray = new int[size]; // initializing array with dynamic size
for (int i = 0; i < size; i++) {
std::cout << "Enter value: ";
std::cin >> pArray[i];
}
for (int i = 0; i < size; i++) {
std::cout << pArray[i] << std::endl;
}
delete[] pArray;
return 0;
}
Both are nice options to work with, but it's recommended by most using vector<>.