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Matrices #2- Please Help Fellow Programmers!

MazharMustapha (34)
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#include <iostream>
#include <cstdlib>
#include <iomanip>
using namespace std;

char menu(char);
int row, col;

int main()
{
	int temp;
	char op, select;
	
	cout << "Welcome!";
	cout << "\nEnter 2 numbers for the row and column of the matrices:"
	     << "\n(Space in between) ";
	cin >> row >> col;
	
	float A[row][col], B[row][col], C[row][col];
	
	cout << "Input Matrix A values: ";
	for(int b = 0; b < row; b++)
	{
		for(int e = 0; e < col; e++)
		{
			cin >> A[b][e];
		}
	}
	
	cout << "Input Matrix B values: ";
	for(int b1 = 0; b1 < row; ++b1)
	{
		for(int e1 = 0; e1 < col; ++e1)
		{
			cin >> B[b1][e1];
		}
	}
	
	do
	{
		select = menu(op);
		if(select == '?')
		{
			menu(op);
		}
		if(select == 'i')
		{
			cout << "\nEnter 2 numbers for the row and column of the matrices:"
	     		 << "\n(Space in between) ";
			cin >> row >> col;
			
			cout << "Input Matrix A values: ";
			for(int b = 0; b < row; b++)
			{
				for(int e = 0; e < col; e++)
				{
					cin >> A[b][e];
				}
			}
	
			cout << "Input Matrix B values: ";
			for(int b1 = 0; b1 < row; ++b1)
			{
				for(int e1 = 0; e1 < col; ++e1)
				{
					cin >> B[b1][e1];
				}
			}
		}
		if(select == 'a')
		{
			for (int c = 0; c < row; ++c)
			{
				for (int c1 = 0; c1 < col; ++c1)
				{
					C[c][c1] = A[c][c1] + B[c][c1];
				}
			}
			for (int i = 0; i < row; i++)
			{
				for(int j = 0; j < col; j++)
				{
					cout << A[i][j] << "   ";
				}
				for(int j = 0; j < col; j++)
				{
					cout << B[i][j] << "   ";
				}
				for(int j = 0; j < col; j++)
				{
					cout << "\t";
					cout << C[i][j] << "   ";
				}
				cout << endl;
			}
		}
		
		if(select == 's')
		{
			for (int c2 = 0; c2 < row; ++c2)
			{
				for (int c3 = 0; c3 < col; ++c3)
				{
					C[c2][c3] = A[c2][c3] - B[c2][c3];
				}
				
			}
			for (int i = 0; i < row; i++)
			{
				for(int j = 0; j < col; j++)
				{
					cout << A[i][j] << "   ";
				}
				for(int j = 0; j < col; j++)
				{
					cout << B[i][j] << "   ";
				}
				for(int j = 0; j < col; j++)
				{
					cout << "\t";
					cout << C[i][j] << "   ";
				}
				cout << endl;
			}
		}
		if (select == 'm')
		{
			for(int i=0;i<row;i++)
			{
				for(int j=0;j<col;j++)
				{
					C[i][j] = 0;
					for(int k=0;k<col;k++)
					C[i][j] = C[i][j] + (A[i][k]*B[k][j]);
				}
			}
			for (int i = 0; i < row; i++)
			{
				for(int j = 0; j < col; j++)
				{
					cout << A[i][j] << "   ";
				}
				for(int j = 0; j < col; j++)
				{
					cout << B[i][j] << "   ";
				}
				for(int j = 0; j < col; j++)
				{
					cout << "\t";
					cout << C[i][j] << "   ";
				}
				cout << endl;
			}
		}
		if(select == 't')
		{
			for (int i = 0; i < row; i++)
			{
				for(int j = 0; j < col; j++)
				{
					cout << A[i][j] << "   ";
					if(j == (col-1))
					{
						cout << endl;
					}
				}
			}
			cout << endl;
			for (int i = 0; i < row; i++)
   			{
      			for (int j = i+1; j < col; j++)
      			{
				  temp=A[i][j];
         		  A[i][j]=A[j][i];
         		  A[j][i]=temp;
      			}
        	}
        	for (int i = 0; i < row; i++)
			{
				for(int j = 0; j < col; j++)
				{
					cout << A[i][j] << "   ";
					if(j == (col-1))
					{
						cout << endl;
					}
				}
			}
        	
		}
	}
	while (select != 'q');
	
	return 0;
}

char menu(char operation)
{
	cout << "Welcome to the Menu!"; 
	cout << "\n? menu "
		 << "\ni input"
		 << "\na addition"
		 << "\ns subtraction"
		 << "\nm multiplication"
		 << "\nt transpose"
		 << "\nq quit program"; 
		 
	cout << "\n\nInput the symbol for your desired operation: ";
	cin >> operation;
	return operation;
}


Welcome!
Enter 2 numbers for the row and column of the matrices:
(Space in between) 2 2
Input Matrix A values: 1 2 3 4
Input Matrix B values: 1 2 3 4
Welcome to the Menu!
? menu
i input
a addition
s subtraction
m multiplication
t transpose
q quit program

Input the symbol for your desired operation: a
1   2   1   2           2       4
3   4   3   4           6       8
Welcome to the Menu!
? menu
i input
a addition
s subtraction
m multiplication
t transpose
q quit program

Input the symbol for your desired operation: s
1   2   1   2           0       0
3   4   3   4           0       0
Welcome to the Menu!
? menu
i input
a addition
s subtraction
m multiplication
t transpose
q quit program

Input the symbol for your desired operation: m
1   2   1   2           7       10
3   4   3   4           15      22
Welcome to the Menu!
? menu
i input
a addition
s subtraction
m multiplication
t transpose
q quit program

Input the symbol for your desired operation: t
1   2
3   4

1   3
2   4
Welcome to the Menu!
? menu
i input
a addition
s subtraction
m multiplication
t transpose
q quit program

Input the symbol for your desired operation: i

Enter 2 numbers for the row and column of the matrices:
(Space in between) 3 3
Input Matrix A values: 1 2 3 4 5 6 7 8 9
Input Matrix B values: 1 2 3 4 5 6 7 8 9
Welcome to the Menu!
? menu
i input
a addition
s subtraction
m multiplication
t transpose
q quit program

Input the symbol for your desired operation: a
1   2   4   1   2   4           2       4       8
4   5   7   4   5   7           8       10      14
7   8   9   7   8   9           14      16      18
Welcome to the Menu!
? menu
i input
a addition
s subtraction
m multiplication
t transpose
q quit program

Input the symbol for your desired operation:


//How come when I enter new values for the 3 x 3 matrix, some of the values are incorrect?
keskiverto (10402)
This is your code:
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int row, col;
cin >> row >> col;

float A[row][col];  // Error 1

cin >> row >> col; // Error 2

cout << "Input Matrix A values: ";
for(int b = 0; b < row; b++)
{
	for(int e = 0; e < col; e++)
	{
		cin >> A[b][e];
	}
}

Error 1: the C++ standard requires that the size of statically allocated array is known during compilation. You have to use dynamic allocation, or allocate "big enough" static array and check that user-given row,col do not exceed that.

Error 2: Changing these variables does not resize the array.
MazharMustapha (34)
What do i do so that when i change the dimensions and enter new values the values are correct?
keskiverto (10402)
Arrays other than one-dimensional are a bit tricky. There are third-party math libraries that do provide matrix-types and usual operations for them.

You could use a resizeable 1D array:
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std::size_t row, col;
cin >> row >> col;

std::vector<float> A( row * col );

cin >> row >> col;

A.resize( row * col );

cout << "Input Matrix A values: ";
for ( int b = 0; b < row; b++ )
{
	for ( int e = 0; e < col; e++ )
	{
		cin >> A[ b*col + e ];
	}
}


Btw, can you tell how these differ:
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// A
        	for (int i = 0; i < row; i++)
			{
				for(int j = 0; j < col; j++)
				{
					cout << A[i][j] << "   ";
					if(j == (col-1))
					{
						cout << endl;
					}
				}
			}

// B
        	for (int i = 0; i < row; i++)
			{
				for(int j = 0; j < col; j++)
				{
					cout << A[i][j] << "   ";
				}
				cout << endl;
			}
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