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# Lec04 - CS1101Y Programming Methodology Control Statements...

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Control Statements. Loops Lecture 4 — September 1, 2008 CS1101Y: Programming Methodology

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September 1, 2008 CS1101Y--group2, Lecture 4 2 Outline while Loop do Loop for Logical Operator boolean Variables • Testing and Debugging
September 1, 2008 CS1101Y--group2, Lecture 4 3 while Loop pseudocode syntax while <condition> <statement(s)> Java syntax while ( <condition> ) { <statement(s)> } ± Use a loop statement if you need to do the same thing repeatedly.

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September 1, 2008 CS1101Y--group2, Lecture 4 4 while Loop •W r i t e a main method that finds the sum of user-entered integers where -99999 is a sentinel value. public static void main(String[] args) { Scanner stdIn = new Scanner(System.in); int sum = 0; // sum of user-entered values int x; // a user-entered value System.out.print("Enter an integer (-99999 to quit): "); x = stdIn.nextInt(); while (x != -99999) { sum = sum + x; System.out.print("Enter an integer (-99999 to quit): "); x = stdIn.nextInt(); } System.out.println("The sum is " + sum); } // end main
September 1, 2008 CS1101Y--group2, Lecture 4 5 do Loop When to use a do loop: – If you know that the repeated thing will always have to be done at least one time. Syntax: do { <statement(s)> } while ( <condition> ); Note: – The condition is at the bottom of the loop (in contrast to the while loop, where the condition is at the top of the loop). – The compiler requires putting a ";" after the ")" . – Proper style dictates putting the "while" part on the same line as the "}"

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September 1, 2008 CS1101Y--group2, Lecture 4 6 do Loop do loop example: – As part of an architectural design program, write a main method that prompts the user to enter length and width dimensions for each room in a proposed house so that total floor space can be calculated for the entire house. After each length/width entry, ask the user if there are any more rooms. Print the total floor space.
September 1, 2008 CS1101Y--group2, Lecture 4 7 for Loop • When to use a for loop: – If you know the exact number of loop iterations before the loop begins. • For example, use a for loop to: – Print this countdown from 10. Sample session : 10 9 8 7 6 5 4 3 2 1 Liftoff! – Find the factorial of a user-entered number . Sample session : Enter a whole number: 4 4! = 24

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September 1, 2008 CS1101Y--group2, Lecture 4 8 for Loop for loop syntax for ( <initialization> ; <condition> ; <update> ) { <statement(s)> } for loop example for (int i=10; i>0; i--) { System.out.print(i + " "); } System.out.println(“Liftoff!”); ± for loop semantics: ± Before the start of the first loop iteration, execute the initialization component. ± At the top of each loop iteration, evaluate the condition component: ± If the condition is true, execute the body of the loop. ± If the condition is false, terminate the loop (jump to the statement below the loop's closing brace). ± At the bottom of each loop iteration, execute the update component and then jump to the top of the loop.
September 1, 2008 CS1101Y--group2, Lecture 4 9 for Loop • Trace this code fragment with an input value of 3.

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Lec04 - CS1101Y Programming Methodology Control Statements...

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