Lesson 6 Selection Structures

Example program //This will convert a numeric grade into a letter grade import TerminalIO.KeyboardReader; public class Grades { public static void main (String args []) { //Variables double grade1,grade2, grade3, total; //End of Variables //Input KeyboardReader reader = new KeyboardReader(); System.out.print ("Please enter in the first grade: "); grade1 = reader.readDouble(); System.out.print ("Please enter in the second grade: "); grade2 = reader.readDouble(); System.out.print ("Please enter in the third grade: "); grade3 = reader.readDouble(); //End of Input //Calculations total = (grade1 + grade2 + grade3) / 3.0; System.out.println ("The average is: "+total); //End of Calculations //If Statements if (total >= 94) System.out.println ("The letter grade is: A"); if (total >= 84 && total <94) System.out.println ("The letter grade is: B"); if (total >= 76 && total <84) System.out.println ("The letter grade is: C"); if (total >= 68 && total <76) System.out.println ("The letter grade is: D"); if (total <68) System.out.println ("The letter grade is: F"); }

Compound Assignment Operations Simple Assignment Compound Addition Compound Subtraction Compound Multiplication Compound Division Compound Remainder = += -= *= /= %= (integers only)

Compound Assignment Equalities x = x + 10 x = x – 10 x = x * 10 x = x / 10 x = x % 10 x += 10 x –= 10 x *= 10 x /= 10 x %= 10

Compound Assignments Translate the following statements to equivalent statements that use extended assignment operators: a. X *=2a. X = X *2; b. Y = Y % 2; b. Y %= 2

Math Class The math class is quite extensive but we will concentrate a just a few of it’s properties: static int abs(int x)Returns the absolute value of an integer x static double abs (double x)Returns the absolute value of a double x static double pow(double base, double exponent) Returns the base raised to the exponent. static long round (double x)Returns x rounded to the nearest whole number. static int max (int a, int b)Returns the greater of a and b static int min(int a, int b)Returns the lesser of a and b static double sqrt (double x)Returns the square root of x.

Examples of Math Class Methods int m; double x; m = Math.abs(-7) // m equals 7 x = Math.abs(-7.5)// x equals 7.5 x = Math.pow(3.0,2.0)// x equals 3.0^2.0 = 9.0 x = Math.pow(16.0,.25)// x equals 16.0 ^.25 = 2.0 m = Math.max(20,40)// m equals 40 m = Math.min(20,40)// m equals 20 m = (int) Math.round(4.27)// m equals 4

Round to two decimal places (double) Math.round(answer*100)/100

Math Class //Given the area of a circle, compute its radius. double area = 10.0, radius; radius = Math.sqrt(area / Math.PI); Math.PI is accurate to about 17 decimal places

Random Class The Random class has two methods that will generate a random integer or double. MethodWhat is Does int nextInt(int n)Returns a integer chosen at random from among 0,1,2,3,…,n-1 double nextDouble()Returns a double chosen at random between 0.0 and 1.0, inclusive.

Example of Random Class Methods Import java.util.Random; Random generator = new Random(); int i; double j; i = generator.nextInt(3);// would give a // random number 0,1, or 2. j = generator.nextDouble();// would give a // random number // between 0 and 1

Control Structures A control structure is simply a pattern for controlling the flow of a program module. The three fundamental control structures of a structured programming language are sequence, selection, and iteration. Sequence control structure is what you have been doing up until now. The second two is what we are going to take a look at next.

Selection/Iteration Structure Selection and Iteration allow the flow of the program to be altered, depending on one or more conditions. Selection is implemented by using a if, if/else, and switch statements. Iteration is implemented by using the while, do/while, and for statements.

The IF statement The if statement works much the same as a if/then statement in Visual Basic. It uses relational operators to test if something is true or false. If it is true, the program will execute the statement(s) within the if statement. If it is false, the program will bypass the statements and continue with the statements following the if statement.

Syntax of the If Statement if (test expression) { statement1; statement2; statementn; } //this is an example of a compound statement

IF/ELSE Statement The IF/ELSE statement works in the same manner as the if/then/else in Visual Basic. It is considered a double-alternative statement. If the expression evaluates as true, then the statements inside the if are executed. If the expression evaluates as false, then the statements inside the else are executed.

Syntax for if/else if (test expression) { statement1; statement2; statementn; } else { statement1; statement2; statementn; } //example of compound statements

Relational Operators Relational operators allow two quantities to be compared. = =Equal to ! =Not equal to <Less than < =Less than or equal >Greater than > =Greater than or equal

Logical Operators

Switch Statement The switch statement works in the same manner as the case select statement in Visual Basic. A selector variable is first evaluated to produce a value. The selector is then compared to a series of cases. If the selector value matches one of the case values, the corresponding case statements are executed.

Syntax for a Switch Statement switch (selector variable) //must be int or char { case case1value :case1statements; break; case case2value :case2statements; break; case casenvalue : case_N_statements; break; default : case exception statements; }

Escape Sequences \b \t \n \” \’ \\ Backspace Tab Newline or line feed Double Quote Single Quote Backslash

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