This Code works only for small number of matrix size.

This code is supposed to find the product of 2 matrices of which the size is entered by the user at runtime. MY code is working fine for small inputs of size of matrix say 2x2 or 3x3 if I put size more than 3 in any of the four field(row1,col1,row2,col2) it crashes. I am a beginner. And the reason I have used pointer scripting instead of subscript  is that it was the requirement for the  assignment.Also, where can I use delete command. Here is the code:
#include<iostream>
using namespace std;

int **multiply(int ** &mat1,int** &mat2,int row1,int col1,int col2,int row2)
{
	int temp = 0;
	//creating the resultant array 
	int **res_mat = new int*(&row1);  // row1 x col2 will be the size of resultant matrix
	for (int i = 0; i < row1; i++)
	{
		*((res_mat)+i) = new int(col2);
	}

	for (int i = 0; i < row1; ++i)
	{

		for (int j = 0; j < col2; ++j)
		{
			*(*(res_mat + i) + j) = 0;
		}
	}
	cout<<endl << "Calculating!!!\n"<<endl;
	for (int i = 0; i < row1; ++i)
	{
		_beep(500, 100);
		for (int j = 0; j < col2; ++j)
		{
			_beep(5000, 100);
			for (int k = 0; k < col1; ++k)
			{
				_beep(1000, 100);
				*(*(res_mat + i) + j) += *(*(mat1 + i) + k) * (*(*(mat2 + k) + j));
				cout << res_mat[i][j]<<endl;
			}
		}
	}
	return res_mat;
	
}

void displayMatrix(int** mat, int row1, int col2)
{
	for (int i = 0; i < row1; i++)  //i=row2
	{
		for (int j = 0; j < col2; j++)  //j=col2
		{
			cout << *(*(mat + i) + j) << '\t';

		}
		cout << endl;
	}



}
int main()
{
	int row1 = 0,
		col1 = 0,
		row2 = 0,
		col2 = 0;
	
	do
	{
		cout << "The number of columns in the first matrix must be equal to the number of rows in the second matrix.\n\n";
		cout << "Rows in matrix 1: ";
		cin >> row1;
		cout << "Columns in matrix 1: ";
		cin >> col1;
		cout << endl << endl;

		cout << "Rows in matrix 2: ";
		cin >> row2;
		cout << "Columns in matrix 2: ";
		cin >> col2;
		cout << endl << endl;
		if (col1 != row2)
			cout << "Error!!!\n\nPlease follow the Instructions: ";
	} while (col1 != row2);

	

	int **mat1 = new int*(&row1);    // creates first matrix
	for (int i = 0; i < row1; i++)
	{
		*((mat1) + i) = new int(col1);
	}
	
	int **mat2 = new int*(&row2); // creates second matrix
	for (int i = 0; i < row2; i++)
	{
		*((mat2)+i) = new int(col2);
	}


	//*********** taking input in matrix 1************
	cout << "\t\t*********** Input in matrix 1************\n\n";
	for (int i = 0; i < row1; i++)  //i=row1
	{
		for (int j = 0; j < col1; j++)  //j=col1
		{
			cout << "Enter [" << i
				<< "][" << j << "] : ";
			cin >> *(*(mat1 + i) + j);
		}
	}

	//*********** taking input in matrix 2************
	cout << "\t\t*********** Input in matrix 2************\n\n";
	for (int i = 0; i < row2; i++)  //i=row2
	{
		for (int j = 0; j < col2; j++)  //j=col2
		{
			cout << "Enter [" << i
				<< "][" << j << "] : ";
			cin >> *(*(mat2 + i) + j);
		}
	}
	system("cls");
	int **reciever;
	reciever = multiply(mat1, mat2, row1, col1, col2, row2);
	
	displayMatrix(reciever, row1, col2);
	cout << endl << endl;

	//deleting the matrices
	/*for (int i = 0; i < row1; i++)
		delete[](*mat1 + i);
	delete[]mat1;

	for (int i = 0; i < row2; i++)
		delete[](*mat2 + i);
	delete[]mat2;
	*/

	/*for (int i = 0; i < row1; i++)
		delete[](*reciever + i);
	delete[]reciever;*/



	return 0;
}

Posted by userNotDead 2020-06-24 02:02:41

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