Why is this segment faulting?

[ashworcp]

The program runs and everything but for values in the list more than 100 it segment faults... The purpose of this program is to run Insertionsort only if the list size is less than the threshold; for all other sizes, the program will run both mergesort and quicksort otherwise. Also, the number of comparisons made by the sorting algorithms will be displayed. Any help would be appreciated.

#include <iostream>
   using namespace std;
   int icount = 0;
   int mcount = 0;
   int qcount = 0;
   
void insertionSort(int x[],int length) {
  int key,i;
  for(int j=1;j<length;j++) {
     key=x[j];
     i=j-1;
     while(x[i]>key && i>=0) {
	    x[i+1]=x[i];
		i--;
     }
     x[i+1]=key;
     icount++;
  }
}   
   
   
void merge(int a[], int Low, int Mid, int High);

void mergeSort(int a[], int Low, int High) {
     int Mid;
          
     if(Low < High) {
     Mid = (Low + High)/2;
     
     mergeSort(a, Low, Mid); 
     mergeSort(a, Mid+1, High);
     merge(a, Low, Mid, High);
     }
}


void merge(int a[], int Low, int Mid, int High) {
     int h = Low;
     int i = Low;
     int j = Mid+1;
     int b[100];
     int k;
     
     while( (h<=Mid) && (j<=High) ) 
     {
            if(a[h]<=a[j]) 
            {
                b[i]=a[h];
                h++;
                mcount++;
            }
            else
            {
                b[i]=a[j];
                j++;
                mcount++;
            }
            i++;
     }
     
     if(h>Mid) 
     {
            for(k = j; k<=High; k++)
            {
                  b[i] = a[k];
                  i++;
            }
            mcount++;
     }
     
     else
     {
            for( k = h; k<=Mid; k++)
            {
                 b[i] = a[k];
                 i++;
            }
            mcount++;
     }
     
     for(k=Low; k<=High; k++)
     {
            a[k] = b[k];
     }
}   
   
void quickSort(int arr[], int left, int right) {
      int i = left, j = right;
      int tmp;
      int pivot = arr[(left + right) / 2];
 
      /* partition */
      while (i <= j) {
            while (arr[i] < pivot)
                  i++;
                  qcount++;
            while (arr[j] > pivot)
                  j--;
                  qcount++;
            if (i <= j) {
                  tmp = arr[i];
                  arr[i] = arr[j];
                  arr[j] = tmp;
                  i++;
                  j--;
                  qcount++;
            }
      };
 
      /* recursion */
      if (left < j)
            quickSort(arr, left, j);
      if (i < right)
            quickSort(arr, i, right);
}   
   

int main() {
	srand(time(NULL));
	char keepGoing = 'y';

	while (keepGoing=='y') {


	// Collect info from user //

	   int thresholdValue;
	   int sizeOfList;
	   int autoList;
	   char displayList;
	   char comp;
	   cout << "" << endl;
	   cout << "Welcome to the Group 13's Sorting Program" << endl << endl;
	   cout << "This program will sort your lists using three different" <<
			"sorting algorithms dependent on the amount of items: Merge Sort," << 
			" QuickSort, and Insertion Sort."<< endl << endl;
	   cout << "To begin, please enter your threshold value: ";
	   cin >> thresholdValue;
	   cout << endl << "Please enter the size of your list: ";
	   cin >> sizeOfList;
	   int list_Values[sizeOfList];
	   int list_Values2[sizeOfList];
	   if (sizeOfList<=100) {
		cout << endl << "Would you like this list to be entered manually (Enter 0) or " <<
			"generated randomly by this program (Enter 1)?: ";
		cin >> autoList;
			if (autoList==0) {
				int counter = 0;
				cout << endl << "Please enter your values one line at a time." << endl;
				while (counter < sizeOfList) {
					cin >> list_Values[counter];
					list_Values2[counter] = list_Values[counter];
					counter++;
				}
			}
			if (autoList==1) {
				cout << endl << "Would you like the program to display the unsorted list? (y/n): ";
				cin >> displayList;
				if (displayList == 'y') {
                    cout << endl;
					for (int i=0; i<sizeOfList; i++) {
						list_Values[i] = (rand()%100)+1;
						list_Values2[i] = list_Values[i];
						cout << list_Values[i] << ", ";
					}
					cout << endl;
				}
				if (displayList == 'n') {
					for (int i=0; i<sizeOfList; i++) {
						list_Values[i] = (rand()%100)+1;
						list_Values2[i] = list_Values[i];
					}
				}
			}
		
		}
	   if (sizeOfList>100) {
			cout << endl << "The unsorted list will be randomly generated and not displayed." << endl;
			for (int i=0; i<sizeOfList; i++) {
				list_Values[i] = (rand()%100)+1;
				list_Values2[i] = list_Values[i];
			}
	   }
	   
	    cout << endl << "Would you like to see the number of comparisons made once sorted? (y/n)" << endl;
        cin >> comp;

	// Done collecting info from user //

	// Begin sorting //

 
		if (sizeOfList <= thresholdValue) {
			cout << endl << "Using Insertion Sort";
			insertionSort(list_Values,sizeOfList);
			cout << endl;
			for (int i=0; i<sizeOfList; i++) {
				cout << list_Values[i] << ", ";
			}
			cout << endl;
			if(comp == 'y') cout << "Number of comparisons: " << icount << endl;
		}
		
		
		else {
		
			// Sort using Quicksort & Mergesort, use the second list (list_Values2) that we stored since the
			// original will be altered.
			quickSort(list_Values,0, sizeOfList);
			mergeSort(list_Values2,0,sizeOfList);
			
		//	if (displayList == 'y') {
				cout << endl << "Sorted using QuickSort" << endl;
				for (int i=0; i<sizeOfList; i++) {
					cout << list_Values[i] << ", ";
                }
	            cout << endl;
				if(comp == 'y') cout << "Number of comparisons: " << qcount << endl;
				cout << endl << "Sorted using MergeSort" << endl;
				for (int i=0; i<sizeOfList; i++) {
					cout << list_Values2[i] << ", ";
				}
				cout << endl;
				if(comp == 'y') cout << "Number of comparisons: " << mcount << endl;
			//}
		}

	   cout << endl <<  "Would you like to sort another list? (y/n): ";
	   cin >> keepGoing;
	   
	}
	system("pause");
	return 0;
}