Additional control structures Jan 13 2019 The if else statement The if else statement chooses which of two statements to execute The if else statement has the form if condition statement to execute if true else statement to execute if false Either statement or both may be a compound statement Notice the semicolon after each statement The else part is optional 2 Flowchart for the if else statement true statement 1 condition fals e statement 2 3 The while loop This is the form of the while loop while condition statement If the condition is true the statement is executed then the whole thing is done again The statement is executed repeatedly until the condition becomes false If the condition starts out false the statement is never executed at all 4 Flowchart for the while loop condition true statement fals e 5 The do while loop The syntax for the do while is do any number of statements while condition The while loop performs the test first before executing the statement The do while statement performs the test afterwards As long as the test is true the statements in the loop are executed again 6 Flowchart for the do while loop statement condition true fals e 7 The increment operator adds 1 to a variable It can be used as a statement by itself or within an expression It can be put before or after a variable If before a variable preincrement it means to add one to the variable then use the result If put after a variable postincrement it means to use the current value of the variable then add one to the variable 8 Examples of int a 5 a a is now 6 int b 5 b b is now 6 int c 5 int d c c is 6 d is 6 int e 5 int f e e is 6 f is 5 int x 10 int y 100 int z x y x is 11 y is 101 z is 111 Confusing code is bad code so this is very poor style 9 The decrement operator subtracts 1 from a variable It can be used as a statement by itself or within an expression It can be put before or after a variable If before a variable predecrement it means to subtract one from the variable then use the result If put after a variable postdecrement it means to use the current value of the variable then subtract one from the variable 10 Examples of int a 5 a a is now 4 int b 5 b b is now 4 int c 5 int d c c is 4 d is 4 int e 5 int f e e is 4 f is 5 int x 10 int y 100 int z x y x is 9 y is 99 z is 109 Confusing code is bad code so this is very poor style 11 The for loop The for loop is complicated but very handy Syntax for initialize test increment statement Notice that there is no semicolon after the increment Execution The initialize part is done first and only once The test is performed as long as it is true The statement is executed The increment is executed 12 Flowchart for the for loop initialize condition true statements increment fals e 13 Parts of the for loop Initialize In this part you define the loop variable with an assignment statement or with a declaration and initialization int i 0 i 0 j k Test or condition A boolean condition Examples i 0 1 Just like in the other control statements we have used Increment An assignment to the loop variable or an application of or to the loop variable 14 Example for loops Print the numbers 1 through 10 and their squares for int i 1 i 11 i System out println i i i Print the squares of the first 100 integers ten per line for int i 1 i 101 i System out print i i if i 10 0 System out println 15 Example Multiplication table public static void main String args for int i 1 i 11 i for int j 1 j 11 j int product i j if product 10 System out print product else System out print product System out println 16 Results 1 2 3 4 5 6 7 8 9 10 2 4 6 8 10 12 14 16 18 20 3 6 9 12 15 18 21 24 27 30 4 8 12 16 20 24 28 32 36 40 5 10 15 20 25 30 35 40 45 50 6 12 18 24 30 36 42 48 54 60 7 14 21 28 35 42 49 56 63 70 8 16 24 32 40 48 56 64 72 80 9 18 27 36 45 54 63 72 81 90 10 20 30 40 50 60 70 80 90 100 17 When do you use each loop Use the for loop if you know ahead of time how many times you want to go through the loop Use the while loop in almost all other cases Example Stepping through an array Example Print a 12 month calendar Example Compute the next step in an approximation until you get close enough Use the do while loop if you must go through the loop at least once before it makes sense to do the test Example Ask for the password until user gets it right 18 The break statement Inside any loop the break statement will immediately get you out of the loop It doesn t make any sense to break out of a loop unconditionally you should do it only as the result of an if test Example If you are in nested loops break gets you out of the innermost loop for int i 1 i 12 i if badEgg i break break is not the normal way to leave a loop Use it when necessary but don t overuse it 19 Multiway decisions The if else statement chooses one of two statements based on the value of a boolean expression The switch statement chooses one of several statements based on the value on an integer int byte short or long or a char expression In Java 5 the value can also be an enum 20 Syntax of the switch statement The syntax is switch expression case value1 statements break case value2 statements break more cases default statements break The expression must yield an integer or a character Each value must be a literal integer or character Notice that colons are used as well as semicolons The last statement in every case should be a break I even like to do this in the last case The default case handles every value not otherwise handled 21 Flowchart for switch statement value statement expression value statement value statement value value statement statement 22 Flowchart for switch statement value statement expression value statement value statement value value statement statement Oops If you forget a break one case runs into the next 23 Example switch statement switch cardValue case 1 System out print Ace …
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