Matrix Multiplication - C++ Program

// Mat_Mul1.cpp - This program inputs two matrices, [A] and [B], from a file and then multiplies them:
     // [A][B] = [C]
     // First, the user is prompted to input the sizes of the arrays to be multiplied, M X N, and N X P.
     // The arrays are then created. The entries for all three arrays are input from a text file.
     // The product array, [C], is output to another text file.
     // Written in Visual C++ 2012 Express Edition
     // 7 June 2013
    
     #include <iostream>
     #include <fstream>
     #include <cctype>
     #include <cmath>
     #include <vector>
     #include <float.h>
    
     using namespace std;
    
     typedef vector<vector<double> > C2DArray;
    
     void Matrix_Mult(bool* error_flag, const int mRows, const int nCols, const int pCols, const C2DArray A_Matrix, const C2DArray B_Matrix, C2DArray& C_Matrix) {
     // Routine to compute the product of two matrices: [A][B] = [C]
     // [A] and [B] are inputs, [C] is the product matrix, output.
     // [A] is of size M X N
     // [B] is of size N X P
     // [C] is of size M X P
    
    	 int i = A_Matrix.size(), j = A_Matrix[0].size(), k = B_Matrix[0].size();
    	 double dummy;
    
    	 // Do some double-checks to make sure matrix dimensions are actually what was fed in to this sub-routine.
    	 // If data not consistent, perhaps other problems present too. User should re-check information.
    
    	 if ((j != B_Matrix.size()) || (i != mRows) || (j != nCols) || (k != pCols))  *error_flag = true;
    
    	 // Make sure C matrix is proper size to receive data
    
    	 if ((C_Matrix.size() != i) || (k != C_Matrix[0].size()))  *error_flag = true;
    
    	 if (!(*error_flag)){
    		for (k = 0; k < mRows; k++) { // Do each row of A with each column of B
    			for (i = 0; i < pCols; i++) {
    				dummy = 0.0;
    				for (j = 0; j < nCols; j++) {
    					dummy += A_Matrix[k][j]*B_Matrix[j][i];
    			    } // End for j
    			    C_Matrix[k][i] = dummy;
    			} // End for i
    		} // End for k
    	 }
    
         return;
     } // End Matrix_Mult
    
     int main()
     {char rflag = 0; //Readiness flag 
    
     cout << "                 Mat_Mul1 (7 June 2013)\n";
     cout << "=========================================================================== \n";
     cout << "This program multiplies two matrices, [A] and [B]: [A][B] = [C].\n";
     cout << "[A] is M X N, [B] is N X P, and [C] is M X P\n";
     cout << "The dimensions of the [A] and [B] matrices, M, N, and P, should \n";
     cout << "have been saved beforehand in a file named mulmatdat.\n";
     cout << "mulmatdat should be in the same folder as the Mat_Mul1 executable.\n";
     cout << "The next values of mulmatdat should be the entries for matrix [A],\n";
     cout << "with data for row 1 first, then row 2, then row 3, etc.\n";
     cout << "The entries for the [B] matrix should follow, in the same order.\n";
     cout << "\nThe data is assumed to be of type double. Variables used within this program\n";
     cout << "are type double.\n";
     cout << "\nThe output is written to the file mulmatout.txt.\n";
    
     cout << "\nIs everything ready (are you ready to continue?)? If yes, Enter y. \n";
     cout << "Otherwise Enter any other key. \n";
     cin >> rflag;
    
     if (toupper(rflag) == 'Y') {
    	C2DArray A, B, C; // A, B, and C Matrices
    	int i, j, mDim, nDim, pDim; // Array index variables and matrix dimensions
    	bool erFlag = false;  // Error flag
    
    	ifstream in("mulmatdat.txt", ios::in);
    
    	if (!in) {
             cout << "\nCannot open the input file.\n";
    	     cout << "\nEnter any key to continue. \n";
    	     cin >> rflag;
             return 0;
    	}
    
    	in >> mDim >> nDim >> pDim; //Input the Matrices' dimensions from the file
    	
    	if ((mDim < 1) || (nDim < 1) || (pDim < 1)){
             cout << "\nInvalid dimension entered. Program terminated. \n";
    	     cout << "\nEnter any key to continue. \n";
    	     cin >> rflag;
             in.close(); //Close the input file before terminating
             return 0;
    	}
    
    	ofstream out("mulmatout.txt", ios::out);
    	if (!out) {
             cout << "\nCannot open the output file. Program terminated.\n";
    	     cout << "\nEnter any key to continue. \n";
    	     cin >> rflag;
             in.close(); //Close the input file before terminating
             return 0;
    	}
    
    	// Beginning of try block, if vector re-sizing unsuccessful
    	try {
    
            // Resize the arrays to the appropriate sizes
             A.resize(mDim); // M rows
    	     B.resize(nDim); // N rows
    	     C.resize(mDim); // M rows
             for (i = 0; i < mDim; i++){
                A[i].resize(nDim); // M columns
    	        C[i].resize(pDim); // P columns
             } // End for i
    
    	     for (i = 0; i < nDim; i++){
                B[i].resize(pDim); // P columns
             } // End for i
    
    	} // End of try block
    
    	catch (bad_alloc& xa) { // Catch block, for exceptions
    
             in.close();
             out.close();
             cerr << "\nIn catch block, so an exception occurred: " << xa.what() << "\n";
             cout << "\nEnter any key to continue. \n";
             cin >> rflag;
             return 0;
    
    	} // End of catch block
    
    	for (i = 0; i < mDim; i++){ //Input the A Matrix from the file
             for (j = 0; j < nDim; j++){
               in >> A[i][j];
             }//End for j
    	}//End for i
    
    	for (i = 0; i < nDim; i++){ //Input the B Matrix from the file
             for (j = 0; j < pDim; j++){
              in >> B[i][j];
             }//End for j
    	}//End for i
    
    	in.close(); //Close the input file
    
    	Matrix_Mult(&erFlag, mDim, nDim, pDim, A, B, C);
    
    	if (erFlag){
    	  cout << "Inconsistent data sent to Matrix_Mult routine. Matrix multiplication NOT performed. Check data before running again.\n";
    	}
    	else {
    
    	 out.precision(DBL_DIG);
    
    	 out << "\nThe A matrix follows:\n";
    	 out << "\n";
    	 for (i = 0; i < mDim; i++){
    	  for (j = 0; j < nDim; j++){
    		out << A[i][j] << " ";
    	  } // End for j
    	  out << "\n";
    	 }//End for i
    
    	 out << "\nThe B matrix follows:\n";
    	 out << "\n";
    	 for (i = 0; i < nDim; i++){
    	  for (j = 0; j < pDim; j++){
    		out << B[i][j] << " ";
    	  } // End for j
    	  out << "\n";
    	}//End for i
    
    	 out << "\nThe product matrix, C, follows:\n";
    	 out << "\n";
    	 for (i = 0; i < mDim; i++){
    	  for (j = 0; j < pDim; j++){
    	   out << C[i][j] << " ";
    	  } // End for j
    	  out << "\n";
    	 }//End for i
    
    	 cout << "\nDone! The solution is in the text file mulmatout.txt \n";
    	} // End else !erFlag
    	out.close();
     } //End if rflag = 'Y'
     else cout << "\nNot ready. Try again when ready with information. \n";
     cout << "\nEnter any key to continue. \n";
     cin >> rflag;
     return 0;
     } // End main program.