fix: bouncing ball exercises

18-project-bouncing-ball/exercises/01-find-the-bug/main.go

@@ -0,0 +1,119 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/inancgumus/screen"
+)
+
+// ---------------------------------------------------------
+// EXERCISE: Find the Bug
+//
+//  As I've annotated in the lectures, there is a bug
+//  in this code. Please find the bug and fix it.
+//
+//
+// HINT #1
+//
+//  💀 Read this only if you get stuck.
+//
+//  Print the width*height and the capacity of the drawing buffer
+//  after a single drawing loop ends. You might be surprised.
+//
+//
+// HINT #2
+//
+//  💀 Read this only if you get stuck.
+//
+//  The bug is in the drawing buffer. It doesn't include the
+//  newline and space characters when creating the buffer. So
+//  the buffer is not large enough to hold all the characters.
+//  So new backing arrays are getting allocated.
+//
+// ---------------------------------------------------------
+
+func main() {
+	const (
+		width  = 50
+		height = 10
+
+		cellEmpty = ' '
+		cellBall  = '⚾'
+
+		maxFrames = 1200
+		speed     = time.Second / 20
+	)
+
+	var (
+		px, py int    // ball position
+		vx, vy = 1, 1 // velocities
+
+		cell rune // current cell (for caching)
+	)
+
+	// create the board
+	board := make([][]bool, width)
+	for column := range board {
+		board[column] = make([]bool, height)
+	}
+
+	// create a drawing buffer
+	buf := make([]rune, 0, width*height)
+
+	// clear the screen once
+	screen.Clear()
+
+	for i := 0; i < maxFrames; i++ {
+		// calculate the next ball position
+		px += vx
+		py += vy
+
+		// when the ball hits a border reverse its direction
+		if px <= 0 || px >= width-1 {
+			vx *= -1
+		}
+		if py <= 0 || py >= height-1 {
+			vy *= -1
+		}
+
+		// remove the previous ball
+		for y := range board[0] {
+			for x := range board {
+				board[x][y] = false
+			}
+		}
+
+		// put the new ball
+		board[px][py] = true
+
+		// rewind the buffer (allow appending from the beginning)
+		buf = buf[:0]
+
+		// draw the board into the buffer
+		for y := range board[0] {
+			for x := range board {
+				cell = cellEmpty
+				if board[x][y] {
+					cell = cellBall
+				}
+				buf = append(buf, cell, ' ')
+			}
+			buf = append(buf, '\n')
+		}
+
+		// print the buffer
+		screen.MoveTopLeft()
+		fmt.Print(string(buf))
+
+		// slow down the animation
+		time.Sleep(speed)
+	}
+}

18-project-bouncing-ball/exercises/01-find-the-bug/solution/main.go

@@ -0,0 +1,99 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/inancgumus/screen"
+)
+
+func main() {
+	const (
+		width  = 50
+		height = 10
+
+		cellEmpty = ' '
+		cellBall  = '⚾'
+
+		maxFrames = 1200
+		speed     = time.Second / 20
+
+		// drawing buffer length
+		// *2 for extra spaces
+		// +1 for newlines
+		bufLen = (width*2 + 1) * height
+	)
+
+	var (
+		px, py int    // ball position
+		vx, vy = 1, 1 // velocities
+
+		cell rune // current cell (for caching)
+	)
+
+	// create the board
+	board := make([][]bool, width)
+	for column := range board {
+		board[column] = make([]bool, height)
+	}
+
+	// create a drawing buffer
+	// BUG FIXED!
+	buf := make([]rune, 0, bufLen)
+
+	// clear the screen once
+	screen.Clear()
+
+	for i := 0; i < maxFrames; i++ {
+		// calculate the next ball position
+		px += vx
+		py += vy
+
+		// when the ball hits a border reverse its direction
+		if px <= 0 || px >= width-1 {
+			vx *= -1
+		}
+		if py <= 0 || py >= height-1 {
+			vy *= -1
+		}
+
+		// remove the previous ball
+		for y := range board[0] {
+			for x := range board {
+				board[x][y] = false
+			}
+		}
+
+		// put the new ball
+		board[px][py] = true
+
+		// rewind the buffer (allow appending from the beginning)
+		buf = buf[:0]
+
+		// draw the board into the buffer
+		for y := range board[0] {
+			for x := range board {
+				cell = cellEmpty
+				if board[x][y] {
+					cell = cellBall
+				}
+				buf = append(buf, cell, ' ')
+			}
+			buf = append(buf, '\n')
+		}
+
+		// print the buffer
+		screen.MoveTopLeft()
+		fmt.Print(string(buf))
+
+		// slow down the animation
+		time.Sleep(speed)
+	}
+}

18-project-bouncing-ball/exercises/02-width-and-height/main.go

@@ -5,6 +5,15 @@
 // License: https://creativecommons.org/licenses/by-nc-sa/4.0/
 //
 
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/inancgumus/screen"
+)
+
 // ---------------------------------------------------------
 // EXERCISE: Adjust the width and height automatically
 //
@@ -88,15 +97,6 @@
 //
 // ---------------------------------------------------------
 
-package main
-
-import (
-	"fmt"
-	"time"
-
-	"github.com/inancgumus/screen"
-)
-
 func main() {
 	const (
 		width  = 50
@@ -107,6 +107,12 @@ func main() {
 
 		maxFrames = 1200
 		speed     = time.Second / 20
+
+		// drawing buffer length
+		//
+		// *2 for extra spaces
+		// +1 for newlines
+		bufLen = (width*2 + 1) * height
 	)
 
 	var (
@@ -123,7 +129,7 @@ func main() {
 	}
 
 	// create a drawing buffer
-	buf := make([]rune, 0, width*height)
+	buf := make([]rune, 0, bufLen)
 
 	// clear the screen once
 	screen.Clear()

18-project-bouncing-ball/exercises/02-width-and-height/solution/main.go

@@ -57,8 +57,13 @@ func main() {
 		board[column] = make([]bool, height)
 	}
 
+	// drawing buffer length
+	// *2 for extra spaces
+	// +1 for newlines
+	bufLen := (width*2 + 1) * height
+
 	// create a drawing buffer
-	buf := make([]rune, 0, width*height)
+	buf := make([]rune, 0, bufLen)
 
 	// clear the screen once
 	screen.Clear()

18-project-bouncing-ball/exercises/03-previous-positions/main.go

@@ -72,8 +72,13 @@ func main() {
 		board[column] = make([]bool, height)
 	}
 
+	// drawing buffer length
+	// *2 for extra spaces
+	// +1 for newlines
+	bufLen := (width*2 + 1) * height
+
 	// create a drawing buffer
-	buf := make([]rune, 0, width*height)
+	buf := make([]rune, 0, bufLen)
 
 	// clear the screen once
 	screen.Clear()

18-project-bouncing-ball/exercises/03-previous-positions/solution/main.go

@@ -23,13 +23,14 @@ func main() {
 		maxFrames = 1200
 		speed     = time.Second / 20
 
-		initVx, initVy = 5, 2
+		// initial velocities
+		ivx, ivy = 5, 2
 	)
 
 	var (
-		px, py   int              // ball position
+		px, py   int        // ball position
-		ppx, ppy int              // previous ball position
+		ppx, ppy int        // previous ball position
-		vx, vy   = initVx, initVy // velocities
+		vx, vy   = ivx, ivx // velocities
 
 		cell rune // current cell (for caching)
 	)
@@ -50,8 +51,13 @@ func main() {
 		board[column] = make([]bool, height)
 	}
 
+	// drawing buffer length
+	// *2 for extra spaces
+	// +1 for newlines
+	bufLen := (width*2 + 1) * height
+
 	// create a drawing buffer
-	buf := make([]rune, 0, width*height)
+	buf := make([]rune, 0, bufLen)
 
 	// clear the screen once
 	screen.Clear()
@@ -62,10 +68,10 @@ func main() {
 		py += vy
 
 		// when the ball hits a border reverse its direction
-		if px <= 0 || px >= width-initVx {
+		if px <= 0 || px >= width-ivx {
 			vx *= -1
 		}
-		if py <= 0 || py >= height-initVy {
+		if py <= 0 || py >= height-ivx {
 			vy *= -1
 		}
 

18-project-bouncing-ball/exercises/04-single-dimensional/main.go

@@ -43,13 +43,14 @@ func main() {
 		maxFrames = 1200
 		speed     = time.Second / 20
 
-		initVx, initVy = 5, 2
+		// initial velocities
+		ivx, ivy = 5, 2
 	)
 
 	var (
-		px, py   int              // ball position
+		px, py   int        // ball position
-		ppx, ppy int              // previous ball position
+		ppx, ppy int        // previous ball position
-		vx, vy   = initVx, initVy // velocities
+		vx, vy   = ivx, ivy // velocities
 
 		cell rune // current cell (for caching)
 	)
@@ -70,8 +71,13 @@ func main() {
 		board[column] = make([]bool, height)
 	}
 
+	// drawing buffer length
+	// *2 for extra spaces
+	// +1 for newlines
+	bufLen := (width*2 + 1) * height
+
 	// create a drawing buffer
-	buf := make([]rune, 0, width*height)
+	buf := make([]rune, 0, bufLen)
 
 	// clear the screen once
 	screen.Clear()
@@ -82,10 +88,10 @@ func main() {
 		py += vy
 
 		// when the ball hits a border reverse its direction
-		if px <= 0 || px >= width-initVx {
+		if px <= 0 || px >= width-ivx {
 			vx *= -1
 		}
-		if py <= 0 || py >= height-initVy {
+		if py <= 0 || py >= height-ivy {
 			vy *= -1
 		}
 

18-project-bouncing-ball/exercises/04-single-dimensional/solution/main.go

@@ -23,13 +23,14 @@ func main() {
 		maxFrames = 1200
 		speed     = time.Second / 20
 
-		initVx, initVy = 5, 2
+		// initial velocities
+		ivx, ivy = 5, 2
 	)
 
 	var (
-		px, py   int              // ball position
+		px, py   int        // ball position
-		ppx, ppy int              // previous ball position
+		ppx, ppy int        // previous ball position
-		vx, vy   = initVx, initVy // velocities
+		vx, vy   = ivx, ivy // velocities
 
 		cell rune // current cell (for caching)
 	)
@@ -47,8 +48,13 @@ func main() {
 	// create a single-dimensional board
 	board := make([]bool, width*height)
 
+	// drawing buffer length
+	// *2 for extra spaces
+	// +1 for newlines
+	bufLen := (width*2 + 1) * height
+
 	// create a drawing buffer
-	buf := make([]rune, 0, width*height)
+	buf := make([]rune, 0, bufLen)
 
 	// clear the screen once
 	screen.Clear()
@@ -59,25 +65,22 @@ func main() {
 		py += vy
 
 		// when the ball hits a border reverse its direction
-		if px <= 0 || px >= width-initVx {
+		if px <= 0 || px >= width-ivx {
 			vx *= -1
 		}
-		if py <= 0 || py >= height-initVy {
+		if py <= 0 || py >= height-ivy {
 			vy *= -1
 		}
 
-		// check whether the ball goes beyond the borders
+		// calculate the new and the previous ball positions
-		if px < width && py < height {
+		pos := py*width + px
-			// calculate the new and the previous ball positions
+		ppos := ppy*width + ppx
-			pos := py*width + px
-			ppos := ppy*width + ppx
 
-			// remove the previous ball and put the new ball
+		// remove the previous ball and put the new ball
-			board[pos], board[ppos] = true, false
+		board[pos], board[ppos] = true, false
 
-			// save the previous positions
+		// save the previous positions
-			ppx, ppy = px, py
+		ppx, ppy = px, py
-		}
 
 		// rewind the buffer (allow appending from the beginning)
 		buf = buf[:0]