#include <iostream.h>
// outputs multiplication table mod modulus
// 1711A class, 1997 October 10

int getmodulus();
// prompts then reads modulus

void makeheader(int modulus);
//outputs heading for table


void makelabelrow(int modulus);
//outputs top row of mult table for modulus


void makerow(int row, int modulus);
//outputs row labeled row of mult table for modulus


int modmult(int row,int column, int modulus);
// returns (row*column) % modulus


int main()
{ int modulus, row;

   modulus = getmodulus();
//   cout << modulus;
   makeheader(modulus);
   makelabelrow(modulus);
   row = 0;
   do
	{
	 makerow(row, modulus);
	 row = row + 1;
	 }
   while (row < modulus);
   return 0;
 }

int getmodulus()
{ int modulus, err_count;

  cout << "\n\nEnter a positive integer\n";
  cin >> modulus;
  err_count = 0;
  while ((modulus <= 0)&&(err_count < 3))
	 {err_count++;
	  cout << "\nWarning: the entry was not a positive integer ( > 0)\n";
	  cout << "Try again\n";
	  cin >> modulus;
	  }
 if (modulus > 0)
  return modulus; //normal return
 else
	{cout << "Your input was incorrect, if you had entered 4\n";
	 cout << "the output would be: \n\n\n";
	 return 4;}  //error trapped return
 }



void makeheader(int modulus)
{ cout << "\n\n    Modular multiplication for " << modulus << endl << endl;
  return;
}


void makelabelrow(int modulus)
{ int column;
  cout << "    *";
  column = 0;
  while (column < modulus)
   { cout.width(5);
	 cout << column;
	 column = column + 1;
   };  // end while
   cout << endl;
   return;
} // end makelabelrow


void makerow(int row, int modulus)
{ int column;
	 cout.width(5);
	 cout << row;
	 column = 0;
	 while (column < modulus)
	   { cout.width(5);
		 cout << modmult(row,column,modulus);
		 column = column +1;
		}
	 cout << endl;
	 return ;
} // end makerow

int modmult(int row,int column, int modulus)
{ return (row*column) % modulus;}