Convert user input from int [] to char [] []

Question

I made this program take an int array as input and sort it using quick sort, but I was wondering how I would change this program, which takes char [] [] as input (a string array) and sorts them alphabetically ? It works if theres only one string, but I want to know what if someone wants an array of strings

//following program sorts an array using quicksort alorithm

#include<iostream.h>
#include<conio.h>

void swap(int *a, int *b)   //function to swap elements
{
    int t;
     t = *a;
    *a = *b;
    *b = t;
}

int partition(int arr[], int left, int right)  //function takes last element as pivot and places all smaller elements on left of pivot and greater elements on right
{
    int pivot=arr[right];  //Pivot
    int i= (left-1);      //index of smaller element

    for(int j=left; j<=(right-1); j++)
    {
        if(arr[j]<=pivot)           //if current element is smaller or equal to pivot, theyre swapped
        {
            i++;
            swap(&arr[i], &arr[j]);
        }
    }
    swap(&arr[i+1], &arr[right]);
    return (i+1);
}

void quicksort(int arr[], int left, int right) //left is starting index, right is last index
{
    if(left<right)
    {
        int index=partition(arr,left,right);
        quicksort(arr, left, index-1);      //sort elements before and after partition
        quicksort(arr, index+1, right);
    }
}

void print(int *arr, int size)      //function to print elements in array
{
    for(int i=0; i<size; i++)
    {
        cout<<arr[i]<<" ";
    }
}

int main()
{
    int n;      //to store no. of elements in array
    char ch;   //ch for choice
    do{
        int *arr=NULL;     //dynamic int array
        clrscr();
    cout<<"\nEnter Number of Elements:";
    cin>>n;
    cout<<"\nEnter Elements in Array to be sorted:";
    for(int i=0; i<n; i++)
    {
        cout<<"\nEnter "<<i<<"th element:";
        cin>>arr[i];
    }
    quicksort(arr,0,(n-1));
    cout<<"\nSorted Array= ";
    print(arr,n);
    delete arr;
    cout<<"\nwanna sort again??(y/n):";
    cin>>ch;
    }while(ch=='Y'||ch=='y');
    return 0;
}

Answer 1

The integer version in your code needs int *arr = new int[n];to allocate an array of integers.

To do this with an array of strings, declare char **arr = new char*[n];and use strdupchar to assign an array to each row.

qsort , . if(arr[j]<=pivot){} if(strcmp(arr[j], pivot) <= 0){}

void swap(char* &a, char* &b)
{
    char *t = a;
    a = b;
    b = t;
}

int partition(char** arr, int lo, int hi)
{
    int i = lo - 1;
    for(int j = lo; j < hi - 1; j++)
    {
        if(strcmp(arr[j], arr[hi]) < 0)
        {
            i++;
            swap(arr[i], arr[j]);
        }
    }

    if(strcmp(arr[hi], arr[i + 1]) < 0)
        swap(arr[hi], arr[i + 1]);

    return i + 1;
}

void quicksort(char** arr, int const lo, int const hi)
{
    if(lo < hi)
    {
        int p = partition(arr, lo, hi);
        quicksort(arr, lo, p);
        quicksort(arr, p + 1, hi);
    }
}

void print(char **arr, int size)      
{
    for(int i = 0; i<size; i++)
        cout << arr[i] << ", ";
    cout << "\n";
}

int main()
{
    int n;      
    cout << "Enter Number of Elements: ";
    cin >> n;
    cout << "Enter Elements in Array to be sorted:\n";

    char buf[255];

    char **arr = new char*[n];
    for(int i = 0; i < n; i++)
    {
        cout << "Enter " << i << "th element: ";
        cin >> buf;
        arr[i] = strdup(buf);
    }

    quicksort(arr, 0, (n - 1));
    cout << "Sorted:\n";
    print(arr, n);
    cout << "\n";

    for(int i = 0; i < n; i++)
        free(arr[i]); //<=== edit**
    delete[]arr;

    return 0;
}

1: quicksort
2: . strdup free