C/C++ Program to make a digital clock with stars

Intended Output

  O     O   O             O     O O O
  O     O   O     O       O         O
  O     O O O             O         O
  O         O     O       O         O
  O         O             O         O

updating in 15 seconds...

The Plan

1. The clock will be of HH:MM format with 4 numbers + 1 colon to be displayed.
2. Each number will be 3x5 dot matrix + one column for spacing.
3. We shall create a canvas of a blank 2D char array of size ROWS = 5, COLUMNS = (3 + 1), i.e., of size 4 * 5 = 20.
4. Then we shall obtain current system time, and extract four digits: HOUR_TENS, HOUR_UNITS, MIN_TENS, MIN_UNITS.
5. Each of these digits is saved on the canvas (i.e., 2D array), at its position determined by the offset.
6. Finally, the array is printed.
7. If the code doesn't compile, try compiling on Visual Studio Express C++ any version.

Pre-requisites

We are going to use a canvas of 2D array to implement this program. For a better understanding please refer the article(s):

• Draw a circle
• Draw an angle

The Source Code

You can copy paste this directly into your cpp file and compile

#include <iostream>

#include <cstdio>

#include <ctime>

using namespace std;

// COMPILE ON VISUAL STUDIO EXPRESS 2012 
// we shall use 3x5 matrix for each 
// digit. one column is for space 
// between two digits. so total cols per 
// digit = 3 + 1 = 4 
const int COLS = 4;

const int ROWS = 5;

// any symbol is used as the 
// clock char, you can change 
// it to whatever 
const char CLOCK_CHAR = 'O';

// each digit is made of 5x4 = 20 dots 
// the last column is the spacer 
// empty dots are set as 0, filled 
// dots are set as 1 
// example of how 3 is encoded- 
// 1 1 1 0 
// 0 0 1 0 
// 1 1 1 0 
// 0 0 1 0 
// 1 1 1 0 
// combining: 1110-0010-1110-0010-1110 
const char* const codes [] =
{

  // digit 0 
  "11101010101010101110",
  // digit 1 
  "01000100010001000100",
  // digit 2 
  "11100010111010001110",
  // digit 3 
  "11100010111000101110",
  // digit 4 
  "10101010111000100010",
  // digit 5 
  "11101000111000101110",
  // digit 6 
  "11101000111010101110",
  // digit 7 
  "1110001000100010001",
  // digit 8 
  "11101010111010101110",
  // digit 9 
  "11101010111000100010",
  // semi-colon separator 
  "00000100000001000000"
};

// we have to print HH:MM that will 
// be of 5 digits. so canvas is x 5 
char canvas [ROWS][COLS * 5] = {{0}};

// helper function to store a digit 
// at offset from the left most digit 
void storeDigit(int digit, int offset);

int main()
{

start:
  // get current system time 
  // this is the c library method 
  // for details check documentation 
  time_t t;

  time(&t);

  tm* local = localtime(&t);

  // hour 0-23 
  int hour = local->tm_hour;

  // min 0-59 
  int min = local->tm_min;

  // HOURS TENS at offset 0 
  storeDigit(hour/10, 0);

  // HOURS UNITS at offset 4 
  storeDigit(hour % 10, 4);

  // COLON at offset 8 
  storeDigit(10, 8);

  // MINS TENS at offset 12 
  storeDigit(min/10, 12);

  // MINS UNITS at offset 16 
  storeDigit(min % 10, 16);

  // display the canvas 
  for(int row = 0; row < ROWS; row++)
  {

    for(int col=0; col < COLS * 5;col++)
    {

      printf("%c ", canvas[row][col]);

    }

    cout << endl;

  }

  cout << "updating in 15 seconds...";

  _sleep(15000);

  system("cls");

  goto start;

  return 0;

}

// definition of the function 
// offsets are- 
// HOURS TENS at offset of 0 
// HOURS UNITS at offset of 4 
// COLON at offset of 8 
// MINS TENS at offset of 12 
// MINS UNITS at offset of 16 
void storeDigit(int digit, int offset)
{

  for(int row = 0; row < ROWS; row++)
  {

    for(int col = 0; col < COLS; col++)
    {

      int x = offset + col;

      int y = row;

      int dot = COLS * row + col;

      if('1' == codes [digit][dot])
      {

        canvas[y][x] = CLOCK_CHAR;

      }

    }

  }

}