ORF 201 COMPUTER METHODS FOR PROBLEM SOLVING Lecture 2 Arithmetic, Simple Loops (C) Princeton University Hello World The file Hello.java Every file must have one public class Point of entry is main() public class Hello { public static void main(String[] args) { All code must System.out.println("Hello, World!"); be in a class } } To compile: To run (execute): Output: javac Hello.java java Hello Hello, World! 2 Fahrenheit to Celsius Anything between /* and */ is ignored by the compiler. /* Program to print a Fahrenheit to Celsius conversion table for fahr = 0, 20, …, 300 */ public class FahrCels { public static void main(String [ ] args) int is the { integer data fahr and cels are instances of int int fahr, celsius; type fahr = 0; celsius = 5 * (fahr-32) / 9; System.out.println(fahr + "\t" + celsius); = is the assignment operator. fahr = 20; celsius = 5 * (fahr-32) System.out.println(fahr . . fahr = 300; celsius = 5 * (fahr-32) System.out.println(fahr Arithmetic operators: +, -, *, / /9; + "\t" + celsius); Statements are executed in sequence. End with semicolon. "\t" is the tab string / 9; + "\t" + celsius); } } 3 Fahrenheit to Celsius 2 /* Program to print a Fahrenheit to Celsius conversion table for fahr = 0, 20, …, 300 */ public class FahrCels2 { public static void main(String [ ] args) { int fahr, celsius; Declare int lower, upper, step; Initialize lower = 0; upper = 300; step = 20; Compute fahr = lower; while (fahr <= upper) { celsius = 5 * (fahr-32) /9; System.out.print(fahr); System.out.print("\t"); System.out.println(celsius); fahr = fahr + step; } } } while (…) {…} Logical operators: <, >, <=, >=, ==, != /* lower limit of temp table */ /* upper limit */ /* step size */ print vs. println 4 Run It To compile: javac FahrCels2.java To run: java FahrCels2 The output: 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 -17 -6 4 15 26 37 48 60 71 82 93 104 115 126 137 148 5 Fahrenheit to Celsius 3 /* Program to print a Fahrenheit to Celsius conversion table for fahr = 0, 20, …, 300 (floating point version) */ import java.text.DecimalFormat; import DecimalFormat gives us DecimalFormat objects public class FahrCels3 { public static void main(String [ ] args) { double fahr, celsius; double vs. float int lower, upper, step; DecimalFormat floating = new DecimalFormat("##,##0.#"); lower = 0; upper = 300; step = 20; } } /* lower limit of temp table */ /* upper limit */ 5/9=0 whereas /* step size */ 5.0/9.0=0.555... fahr = lower; while (fahr <= upper) { celsius = (5.0/9.0) * (fahr-32); System.out.println(floating.format(fahr) + "\t" + floating.format(celsius)); fahr = fahr + step; } Floating.format(x) 6 The Output 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 240.0 260.0 280.0 300.0 -17.8 -6.7 4.4 15.6 26.9 37.8 48.9 60.0 71.1 82.2 93.3 104.4 115.6 126.7 137.8 148.9 7
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