// C++ program for Merge Sort
//C++ program from geeksforgeeks.org
#include <iostream>
#include <time.h>
#include <math.h>
#include <fstream>

using namespace std;

void merge(int leftArray[], int rightArray[], int array[], int leftSize, int rightSize) {
    int i = 0, l = 0, r = 0;

    while (l < leftSize && r < rightSize) {
        if (leftArray[l] < rightArray[r]) {
            array[i] = leftArray[l];
            i++;
            l++;
        } else {
            array[i] = rightArray[r];
            i++;
            r++;
        }
    }

    while (l < leftSize) {
        array[i] = leftArray[l];
        i++;
        l++;
    }

    while (r < rightSize) {
        array[i] = rightArray[r];
        i++;
        r++;
    }
}

void mergeSort(int array[], int length) {
    if (length <= 1) {
        return;
    }

    int middle = length / 2;
    int leftSize = middle;
    int rightSize = length - middle;
    int* leftArray = new int[leftSize];
    int* rightArray = new int[rightSize];

    for (int i = 0; i < length; i++) {
        if (i < middle) {
            leftArray[i] = array[i];
        } else {
            rightArray[i - middle] = array[i];
        }
    }

    mergeSort(leftArray, leftSize);
    mergeSort(rightArray, rightSize);
    merge(leftArray, rightArray, array, leftSize, rightSize);

    delete[] leftArray;
    delete[] rightArray;
}

// Driver code
int main(void)
{
	ifstream inputFile("C:\\Users\\User\\Desktop\\CSDC103 Asis_Lab Exercise #1\\small.txt"); 
	
	if (!inputFile) {
	cerr << "Failed to open the input file." << endl;
	return 1;
	}

	inputFile.close();


	int array[100000];
	int length = 0;
	
	
	// Read integers from the file
    while (length < 100000 && inputFile >> array[length]) { 
        length++;
    }

    inputFile.close(); 



	clock_t start = clock();
	for(int j = 0; j < 10; ++j) {
    
		mergeSort(array, length);

		clock_t end = clock();
		double cpu_time_used = ((double)(end - start)) / CLOCKS_PER_SEC;

		printf("Merge Sort took %f seconds to execute \n", cpu_time_used);
		cout << endl; 
	}

   
 
	
}

// This code is contributed by Mayank Tyagi
// This code was revised by Joshua Estes

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About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}