Function Template - Insertion sort

[mainrole94]

Hi, I am new here. I got this homework due tonight. I have been working on this code for a while. This works fine and compiles but it crashes at run time. I am thinking there might be some problems with my logic here. Please help me. Here is my code.

/*
* Function Template Program
*
* Description: arranges different user input variable types using insertion sort
*
*
*/

#include <iostream>

using namespace std;

template <class T>
void printArray(T arrray[], int n);
template <class T>
void insertionSort(T arrray[], int n);


//function template for printing array elements
template <class S>
void printArray(S a[], int n)
{
    for(int i = 1; i <= n; i++)
        cout << a[i] << " ";
    cout << endl;
}

//function template for sorting array elements
 template <class S>
 void insertionSort(S a[], int n)
{
    S temp = a[0];
    for(int i = 1; i <= n; i++)
    {
        temp = a[i];
        int j = 0;
        for(j = i; j > 0; j--)
            if(temp < a[j - 1])
               a[j] = a[j - 1];
            else break;
        a[j] =  temp;
    }
}


int main(void){

int n;

cout << "This program sorts different variable types" << endl;
cout << endl;

int selection;
cout << "What variable type do you want to sort?" << endl;
cout << "[1] Integer" << endl;
cout << "[2] Float" << endl;
cout << "[3] Character" << endl;
cout << "[4] Double" << endl;
cout << "[5] Exit" << endl;
cin >> selection;


    switch(selection){

        case 1:
            cout << "Please enter array size: ";
            cin >> n;

            cout << "Please enter array elements:" << endl;
            cout << endl;

            int intArray[n];

                for (int i=1; i <= n; i++){

                    cout << "* ";
                    cin >> intArray[i];
                    cout << endl;

                }
                insertionSort(intArray, n);
                cout << endl;
                printArray(intArray, n); break;

            case 2:
                cout << "Please enter array size: ";
                cin >> n;

                  cout << "Please enter array elements." << endl;
                  cout << endl;

                float floatArray[n];

                for (int i=1; i <= n; i++){

                    cout << "* ";
                    cin >> floatArray[i];
                    cout << endl;

                }
                insertionSort(floatArray, n);
                cout << endl;
                printArray(floatArray, n);
                    break;

            case 3:
                cout << "Please enter array size: ";
                cin >> n;


                cout << "Please enter array elements." << endl;
                cout << endl;

                char charArray[n];

                for (int i=1; i <= n; i++){

                    cout << "* ";
                    cin >> charArray[i];
                    cout << endl;

                }
                insertionSort(charArray, n);
                cout << endl;
                printArray(charArray, n);
                    break;

            case 4:
                  cout << "Please enter array size: ";
                  cin >> n;

                  cout << "Please enter array elements." << endl;
                  cout << endl;

                double doubleArray[n];

                for (int i=1; i <= n; i++){

                    cout << "* ";
                    cout << endl;
                    cin >> doubleArray[i];

                }
                insertionSort(doubleArray, n);
                cout << endl;
                printArray(doubleArray, n);
                    break;

        case 5:
                    break;

        default:
                    cout << "Please enter valid selection!" << endl;
                break;

        }
}

[Durwood]

You say this compiles? It doesn't in VS2005 as is. I can make a few changes to make it compile, however. You have a few problems here:

1. "int n" at the top of main() should be a constant expression. This means in this case that it should have a const qualifier in front of it and should reference a concrete number (1000 or 100 for example...)

2. Since you are intending for the value of n to be user entered, this makes 1 somewhat moot, but also means that you cannot use automatic storage for your arrays. You should use pointers instead, i.e. "char *charArray; charArray = new char[ n ];" Then before the break you would do a "delete[] charArray". If you choose to do this then you will need to make each case statement a compound statement block. (i.e. put '{' immediately after the case X: and put a '}' immediately before the "break;".

3. You are looping from 1 to n inclusive... C / C++ arrays go from 0 to n exclusive ( n-1 ). This means you need to change your loop to read "for ( int i = 0; i < n; i++ )" This may not cause a crash (it may as well) but it is certainly incorrect. This goes for ALL of your loops. In addition, if you are counting down in a loop you should do the opposite logically: "for( j = i; j >= 0; j-- )"

Hope this helps...