2 files changed, 81 insertions, 0 deletions
diff --git a/projects/09/Fraction/Fraction.jack b/projects/09/Fraction/Fraction.jack
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+++ b/projects/09/Fraction/Fraction.jack
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+// This file is part of www.nand2tetris.org
+// and the book "The Elements of Computing Systems"
+// by Nisan and Schocken, MIT Press.
+// File name: projects/09/Fraction/Fraction.jack
+
+/** Represents the Fraction type and related operations. */
+class Fraction {
+   field int numerator, denominator;  // field = property = member variable.
+  
+   /** Constructs a (reduced) fraction from the given numerator and denominator. */
+   constructor Fraction new(int x, int y) {
+      let numerator = x;
+      let denominator = y;
+      do reduce();   // reduces the fraction
+      return this;   // a constructor is expected to return a reference to the new object
+   }
+
+   // Reduces this fraction.
+   method void reduce() {
+      var int g;
+      let g = Fraction.gcd(numerator, denominator);
+      if (g > 1) {
+         let numerator = numerator / g;
+         let denominator = denominator / g;
+      }
+      return;
+   }
+
+   /** Accessors. */
+   method int getNumerator() { return numerator; }
+   method int getDenominator() { return denominator; }  
+
+   /** Returns the sum of this fraction and the other one. */
+   method Fraction plus(Fraction other) {
+      var int sum;
+      let sum = (numerator * other.getDenominator()) + (other.getNumerator() * denominator);
+      return Fraction.new(sum, denominator * other.getDenominator());
+   }
+
+   // More fraction-related methods (minus, times, div, etc.) can be added here.
+  
+   /** Disposes this fraction. */
+   method void dispose() {
+      do Memory.deAlloc(this);  // uses an OS routine to recycle the memory held by the object
+      return;
+   }
+   
+   /** Prints this fraction in the format x/y. */
+   method void print() {
+      do Output.printInt(numerator);
+      do Output.printString("/");
+      do Output.printInt(denominator);
+      return;
+   }
+
+   // Computes the greatest common divisor of the given integers.
+   function int gcd(int a, int b) {
+      var int r;
+      while (~(b = 0)) {             // applies Euclid's algorithm
+         let r = a - (b * (a / b));  // r = remainder of the integer division a/b
+         let a = b; let b = r;
+      }
+      return a;
+   }
+}
diff --git a/projects/09/Fraction/Main.jack b/projects/09/Fraction/Main.jack
new file mode 100644
index 0000000..43ddece
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+++ b/projects/09/Fraction/Main.jack
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+// This file is part of www.nand2tetris.org
+// and the book "The Elements of Computing Systems"
+// by Nisan and Schocken, MIT Press.
+// File name: projects/09/Fraction/Main.jack
+
+// Computes the sum of 2/3 and 1/5.
+class Main {
+   function void main() {
+      var Fraction a, b, c;        
+      let a = Fraction.new(2,3);  
+      let b = Fraction.new(1,5);  
+      let c = a.plus(b);  // Computes c = a + b
+      do c.print();       // Prints "13/15"
+      return;
+   }
+}