Additional control structures 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 Flowchart for the if else statement true statement 1 condition fals e statement 2 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 Flowchart for the while loop condition fals e true statement The do while loop The while loop performs the test first before executing the statement The do statement performs the test afterwards As long as the test is true the statements in the loop are executed again The syntax is do any number of statements while condition Flowchart for the do loop statement condition fals e true 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 Examples of int a 5 a a is now 6 int e 5 int f e e is 6 f is 5 int b 5 b b is now 6 int x 10 int y 100 int z x y x is 11 y is 101 z is 111 int c 5 int d c c is 6 d is 6 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 Examples of int a 5 a a is now 4 int e 5 int f e e is 4 f is 5 int b 5 b b is now 4 int x 10 int y 100 int z x y x is 9 y is 99 z is 109 int c 5 int d c c is 4 d is 4 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 Flowchart for the for loop initialize condition fals e true statements increment Parts of the for loop Initialize In this part you define the loop variable with an assignment statement or with a declaration and initialization Examples i 0 1 int i 0 i 0 j k Test or condition A boolean condition 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 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 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 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 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 Example Print a 12 month calendar Use the while loop in almost all other cases Example Repeat Scott s problem until you get to 1 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 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 Even then it s seldom a good idea Example for int i 1 i 12 i if badEgg i break 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 Syntax of the switch statement The expression must yield an integer or a character switch expression case value1 Each value must be a statements literal integer or character break Notice that colons are case value2 statements used as well as semicolons break more cases The last statement in every case should be a break default statements The default case break handles every value not otherwise handled The syntax is Flowchart for switch statement value statement expression value statement value statement value value statement statement Flowchart for switch statement value statement expression value statement Oops If you forget a break one case runs into the next value statement value value statement statement Example switch statement switch cardValue case 1 System out print Ace break case 11 System out print Jack break case 12 System out print Queen break case 13 System out print King break default System out print cardValue break Spaces and indentation The Style guide tells you where to use indentation Rule 5 and spaces Rule 7 Learn and follow these rules Yes we will take off points if you don t Example red blobs indicate tabs and spaces if condition statements The End
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