Question

First assignment for C++. How do I setup this dynamic multiplication table using 2D arrays and double pointers?

The assignment asks to

Write a program that displays a 2D multiplication table based on row and column value specified by the user. Perform a data validation to ensure the number of rows and columns given by the user exist on the interval [1, 10]. If possible, protect against inputs that contain symbols that would normally crash the program (i.e. letter, symbols, numbers containing a decimal point, etc..).

While completing it, you must show your understanding of double pointers (int**), and dynamic memory And also store the internal portion of the table (i.e. the numbers on the inside that represent the products) in a dynamic 2D array (also known as heap memory).

#include
#include
using namespace std;

int main() {

   int row = 0;
   int   col = 0;

   do {
       cout << "Please enter the number of rows on the interval [1, 10]: ";
       cin >> row;
       if (row < 1 || row > 10) cout << "\nThat is not within the range [1-10]. Please try again...\n";
   } while (row < 1 || row > 10);
   do {
       cout << "Please enter the number of columns on the interval [1, 10]: ";
       cin >> col;
       if (col < 1 || col > 10) cout << "\nThat is not within the range [1-10]. Please try again...\n";
   } while (col < 1 || col > 10);

   int** ppRootPointer = NULL;
   ppRootPointer = new(int* [col]);
  
   for (int i = 0; i < col; i++) {
       ppRootPointer[i] = new(int [row]);
   }
   int counter = 1;
   for (int i = 0; i < col; i++) {
       for (int j = 0; j < row; j++) {
           ppRootPointer[i][j] = counter++;
       }
   }

   cout << left;
   for (int i = 0; i < col; i++) {
       for (int j = 0; j < row; j++) {
           cout << ppRootPointer[i][j];
       }
       cout << endl << endl;

       cout << left;
       for (int i = 0; i < col; i++) {
           for (int j = 0; j < row; j++) {
               cout << *(*(ppRootPointer + i) + j);
           }
           cout << endl;
       }
       cout << endl << endl;

       for (int i = 0; i < col; i++) {
           delete[] ppRootPointer[i];
       }
       delete[] ppRootPointer;

   }
  

     

for(int i = 0; i <= col; i++){
if(i == 0){
cout << " ";
continue;
}
cout << "|" << i;
}
for(int i = 1; i <= row; i++){
cout << "\n---";
for(int j = 1; j <= col; j++){
cout << "+---";
}
cout << "\n";
cout << i;
for(int j = 1; j <= col; j++){
cout << "|" << i * j;
}
}
cout << "\n";
}

Answer 1

// C++ program to print multiplication table using 2D array

#include <iostream>

#include <limits>

#include <iomanip>

using namespace std;

int main() {

       int row,col;

       int i,j;

       int **mulTable = NULL; // define the multiplication table

       // input of number of rows

       cout << "Please enter the number of rows on the interval [1, 10]: ";

       cin>>row;

       // validate row and re-prompt until valid value is entered

       while(cin.fail() || row < 1 || row > 10)

       {

             cin.clear(); // back in 'normal' operation mode

             cin.ignore(std::numeric_limits<std::streamsize>::max(),'\n'); // and remove the bad input

             cout << "That is not within the range [1-10]. Please try again : ";

             cin>>row;

       }

       // input of number of columns

       cout<<"Please enter the number of columns on the interval [1, 10]: ";

       cin>>col;

       // validate col and re-prompt until valid value is entered

       while(cin.fail() || col <1 || col > 10)

       {

             cin.clear(); // back in 'normal' operation mode

             cin.ignore(std::numeric_limits<std::streamsize>::max(),'\n'); // and remove the bad input

             cout << "That is not within the range [1-10]. Please try again : ";

             cin >> col;

       }

       // create multiplication table of rows row and columns col

       mulTable = new int*[row];

       for(i=0;i<row;i++)

       {

             mulTable[i] = new int[col];

             for(j=0;j<col;j++)

                    mulTable[i][j] = (i+1)*(j+1);

       }

       // print the multiplication table

       cout<<endl<<endl<<"Multiplication Table : "<<endl;

       for(j=0;j<=col;j++)

       {

                    cout<<"+-----";

       }

       cout<<"+"<<endl;

       cout<<"|"<<left<<setw(5)<<"";

       for(j=0;j<col;j++)

       {

             cout<<"|"<<left<<setw(5)<<(j+1);

       }

       cout<<"|"<<endl;

       for(j=0;j<=col;j++)

       {

             cout<<"+-----";

       }

       cout<<"+";

       for(i=0;i<row;i++)

       {

             cout<<endl<<"|"<<left<<setw(5)<<(i+1);

             for(j=0;j<col;j++)

                    cout<<"|"<<left<<setw(5)<<mulTable[i][j];

             cout<<"|"<<endl;

             for(j=0;j<=col;j++)

             {

                    cout<<"+-----";

             }

             cout<<"+";

       }

       cout<<endl;

       // delete the memory allocated

       for(int i=0;i<row;i++)

             delete [] mulTable[i];

       delete [] mulTable;

       return 0;

}

//end of program

Output: