Additional control structuresThe if-else statementFlowchart for the if-else statementThe while loopFlowchart for the while loopThe do-while loopFlowchart for the do loopThe increment operatorExamples of ++The decrement operatorExamples of --The for loopFlowchart for the for loopParts of the for loopExample for loopsExample: Multiplication tableResultsWhen do you use each loop?The break statementMultiway decisionsSyntax of the switch statementFlowchart for switch statementSlide 23Example switch statementSpaces and indentationThe EndAdditional control structuresThe 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 optionalFlowchart for the if-else statementcondition?truestatement-1 statement-2falseThe 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 allFlowchart for the while loopcondition?statementtruefalseThe 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 loopcondition?statementtruefalseThe 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 variableExamples 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 111The 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 variableExamples 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 109The 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 executedFlowchart for the for loopcondition?statementstruefalseincrementinitializeParts 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 int i = 0 i = 0, j = k + 1•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 variableExample 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 100When 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 rightThe 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 expressionSyntax 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;•The default: case handles every value not otherwise handledFlowchart for switch statementexpression?statement statementstatementstatementstatementvaluevaluevaluevaluevalueFlowchart for switch statementOops: If you forget a break, one case runs into the next!expression?statement
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