You can use args.length to get the number of elements in the array.

I think you need to throw by like this

 public Complex readInput()
 {
     Complex temp = 0;
     try
     {
          Console.Write("Enter input: ");
          string input = Console.ReadLine();

          String[] cplx= input.Split(' ');
          if (cplx.Length >= x)
          {
               throw new IndexOutOfRangeException("INVALID INPUT ENTRY...");
          }

          temp = new Complex(Double.Parse(cplx[0]), Double.Parse(cplx[1]), ...);
     }
     catch (FormatException)
     {
          Console.WriteLine("INVALID INPUT ENTRY...");
     }
     return temp;
 } 

The problem happens here:

mStars = new int[_numReviews];


for (int i = 0; i <= _numReviews; ++i) {

Specifically here:

i <= _numReview // this causes you to go out of bounds

changing it to:

i < _numReview

resolves the issue

You are allocating _numReview items. C++ has 0-based array indexing. Elements will go from 0 to _numReview - 1

Please consider using std::string and std::vector instead of c-style arrays.

The real reason is in V8 memory optimization. When you store integers - it stores the 32 bit number in place, But when you store double-number - it is stored differently (as an object) - so yValues array contains the reference but the actual value stored in heap. So in your example you just used all heap memory. To see the limit, use: console.memory and you'll see something like this:

MemoryInfo {
totalJSHeapSize: 10000000, 
usedJSHeapSize: 10000000, 
jsHeapSizeLimit: 3760000000}

In my browser it is 3_760_000_000

The object on heap takes 50+ bytes, so my limit somewhere around 69_000_000 floating point numbers.