Non-working while loop & Messed up Binary Search - c++

Question

For this program I have to fill an array with 20 random numbers (1-100), sort the array (descending) and then search for a random key value and output the position of that value if it is in the array. I am having 2 problems. First the while loop I have to exit the program is not working and I can not figure out why. Second my binary search is not returning a position value and I don't know why. This code will compile.
#include <iostream>
#include <ctime>
using namespace std;
int printArray(int *arr, int arraySize);
int fillArrayWithRandomNumbers(int *arr, int arraySize);
int bubbleSortDesc(int *arr, int arraySize);
int binarySearch(int *arr, int arraySize, int key);
int main()
{
int const arraySize = 20;
int arr[arraySize];
cout << "CMPSC 201-Extra Credit\n" << "This program fills an array, and then searches for a random key value." << endl <<endl;
char stopTheProgram = 'n';
do {
int key, result;
cout << "Unordered array:" << endl;
fillArrayWithRandomNumbers(arr, arraySize);
printArray(arr, arraySize);
cout << endl << "Array after a bubble sort : " <<endl;
bubbleSortDesc(arr, arraySize);
printArray(arr, arraySize);
key = rand()%100;
cout << endl <<"Searching for " << key << endl;
result = binarySearch(arr, key, arraySize);
if (result == -1)
{
cout << "Key " << key << " not found in the array" << endl;
}
else
{
cout << "Key " << key << " found at position " << result << endl;
}
cout << "Stop the program? (y/n) ";
cin >> stopTheProgram;
cout << endl;
} while (!(stopTheProgram == 'Y' || stopTheProgram == 'y'));
return 0;
}
int fillArrayWithRandomNumbers(int *arr, int arraySize)
{
srand((unsigned)time(NULL));
for (int i = 0; i<arraySize; i++)
{
arr[i] = (rand() % 100) + 1;
}
return *arr;
}
int printArray(int *arr, int arraySize)
{
for (int i = 0; i<arraySize; i++)
{
cout << arr[i] << " ";
}
return *arr;
}
int bubbleSortDesc(int *arr, int arraySize){
int i, j;
int temp = 0;
for (i = 0; i < arraySize; i++)
{
for (j = 0; j < arraySize - 1; j++)
{
if (arr[j] < arr[j + 1])
{
temp = arr[j];
arr[j] = arr[j + 1];
arr[j + 1] = temp;
}
}
}
return *arr;
}
int binarySearch(int arr[], int key, int arraySize)
{
int i, j;
int temp = 0;
for (i = 0; i < arraySize; i++)
{
for (j = 0; j < arraySize - 1; j++)
{
if (arr[j] > arr[j + 1])
{
temp = arr[j];
arr[j] = arr[j + 1];
arr[j + 1] = temp;
}
}
}
int position, lowerBound = 0;
position = (lowerBound + arraySize) / 2;
while ((arr[position] != key) && (lowerBound <= arraySize))
{
if (arr[position] > key)
{
arraySize = position - 1;
}
else
{
lowerBound = position + 1;
}
position = (lowerBound + arraySize) / 2;
}
if (lowerBound <= arraySize)
{
position = 19 - position;
return position;
}
else {
return -1;
}
}
Solved: I now have fixed my problems with my binary search, and exiting my while loop. I am going to leave this here just in case anyone has my prof after me. So just to recap, this program fills an array with 20 random numbers (ranging 1-100), sorts the array in descending order and then creates a random key value (between 1-100). It then bubble sorts the array so it is in ascending order, uses a binary search to find the key value in the array and finally output the position of that key value if it is in the array.

Answer 1

I can see two issues with your code. First, you are shadowing the stopTheProgram variable. You define it once just before the do/while loop and initialize it to 'n'; Then once inside the do/while you define another stopTheProgram. This is a problem because of scoping. Inside the do/while loop the input from the user is assigned to the local stopTheProgram (defined in the do/while) but that ceases to exits outside the loop. So the while loop expression is always evaluated using the globally scoped stopTheProgram, which is set to 'n'. So remove the second definition. Second is an issue with the expression that controls the while loop. It always evaluates true. Draw a truth table if you can't visualize it. If stopTheProgram = 'Y' then the stopTheProgram != "Y" || stopTheProgram != 'y' is 0 || 1 which is always true. If stopTheProgram = 'y' then stopTheProgram != "Y" || stopTheProgram != 'y' is 1 || 0 which is always true. This works: while(!(stopTheProgram == 'Y' || stopTheProgram == 'y'))