dynMult.cpp

/* create an arbitrary multiplication table.
 */
#include <iostream>
#include <iomanip>
#include <cmath>
#include "termmanip.h"

using namespace std;

bool isPrime(int n);

int main() {
  int **table;  //my table
  int rows, cols; //rows and columns
  int maxDigits;
  int maxAnswer;

  //get the number of rows and columnns
  cout << "Rows: ";
  cin >> rows;
  cout << "Cols: ";
  cin >> cols;

  //compute the biggest
  maxAnswer = rows * cols;
  maxDigits = 1;
  maxAnswer /= 10;
  while(maxAnswer){
    maxDigits++;
    maxAnswer/=10;
  }
  
  
  //allocate the row pointers
  table = new int*[rows];

  //allocate the space for all the integers
  table[0] = new int[rows * cols];

  //organize pointers so our simple fleshy brains can handle it!
  for(int i=1; i<rows; i++) {
    table[i] = table[i-1] + cols;
  }

  //populate the table
  for(int i=0; i<rows; i++) {
    for(int j=0; j<cols; j++) {
      table[i][j] = (i+1) * (j+1);
    }
  }

  //print the header
  cout << reverseVideo;
  cout << setw(maxDigits) << ' ';

  for(int col=1; col <= cols; col++) {
    cout << setw(maxDigits+1) << col;
  }
  cout << ' ' << endl;
  cout << normal;

  //print the rows
  for(int i=0; i<rows; i++) {
    cout << reverseVideo;
    cout << setw(maxDigits+1) << "+" << normal;
    for(int j=0; j<cols; j++) {
      cout << setfill('-') << setw(maxDigits+1) << '+';
    }
    cout << setfill(' ') << endl;

    cout << reverseVideo;
    cout << setw(maxDigits) << i+1 << "|";
    cout << normal;
    for(int j=0; j<cols; j++) {
      if(isPrime(table[i][j])) {
	cout << bold << magenta;
      }
      cout << setw(maxDigits) << table[i][j] << normal << "|";
    }
    cout << endl;
  }

  cout << reverseVideo << setw(maxDigits+1) << "+" << normal;
  for(int j=0; j<cols; j++) {
    cout << setfill('-') << setw(maxDigits+1) << '+';
  }
  cout << setfill(' ') << endl;

  return 0;
}


//check primality
bool
isPrime(int n) {
  int sn;
  
  //handle evens
  if(n%2 == 0) {
    if(n == 2) {
      return true;
    } else {
      return false;
    }
  }

  if(n<=1) return false;
  
  //check the others!
  sn = (int) ceil(sqrt(n));
  for(int factor=3; factor<=sn; factor+=2) {
    if(n%factor == 0) return false;
  }

  //if we make it here, n is prime
  return true;
}