Converting User Input from int[] to char[][] - c++

Question

I made this program to take int array as input and sort it using quick sort, but i was wondering, how would i change this program that it takes char[][] as input (string array) and sort them alphabetically?
It works if theres just one string, but i wanna know what if someone wants 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 array of integers.
To do this with array of strings, declare char **arr = new char*[n]; and use strdup to assign array of char to each string.
You should be able to use the standard qsort in older compilers, otherwise use this modified version of your quicksort. The main difference is the replacement of if(arr[j]<=pivot){} with 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;
}
Edit 1: changed quicksort function
Edit 2: changed the cleanup. strdup has to be cleaned up with free