CMT4001 -- Programming Software Applications

Dr. Xiaohong Gao

Repetitions and Methods

Week 4

Contents

To become familiar with repetitions;

To become familiar with while loop;

To become familiar with do loop;

To become familiar with for loop;

To become familiar with nested for loop;

To become familiar with methods;

Repetitions

while Loops

do Loops

for Loops

break and continue

while Loop

The syntax for the while loop is:

while ( continue – condition){ // Loop body}

Example: TestWhile.java

while Loop Flow Chart

Continuecondition ?

Statement(s)

Nextstatement

falsetrue

true

//TestWhile.java

public class TestWhile{ // main method public static void main(String[]args) { int data; int sum = 0; // read an initial data System.out.println(“Enter an int value); data = MyInput.readInt();

// keep reading until the input is 0

while (data !=0) { sum+= data; System.out.println(“Enter an int value, the program exists if the input is 0”); data =MyInput.readInt(); } System.out.println(“ The sum is” + sum); }}

do Loop

• The do loop is a variation of while loop. Its syntax is :

do { // loop body }while(condition)

Example:TestDo.java

do Loop

Statement(s)

Continuecondition ?

Nextstatement

true

false

TestDo.java

// TestDo.java; test the do looppublic class TestDo{ public static void main(String[]args) { int data; int sum = 0; do { data = MyInput.readInt(); sum+= data; }while (data !=0);

TestDo.java

System.out.println(“The sum is “+ sum): }}

The for Loop

The general syntax for for loop is:

for( i= initialValue; i<endValue; i++){ // for loop body}

The for Loop

int i = 0;while (i < 100){ System.out.println("Welcome to Java! ); i++; }

Example:int i;for (i = 0; i<100; i++) { System.out.println("Welcome to Java! ); }

for Loop Flow Chart

The for Loop

i = 0;

i < 100 ?i=++

System.out.println (“Welcome to Java!”);

Nextstatement

TestSum.java

// TestSum.java; Compute sum =0.01+0.02+...+1public class TestSum{ // main method public static void main(String[]args) {//initialize sum float sum = 0; // keep adding 0.01 to sumfor(float i=0; i<=1.0f;i+0.01f) sum+=i;

TestSum.java

// display result

System.out.println(“The sum is “+ sum); }}

Using nested for loops//TestMulTable.java; display a multiplication//table;

public class TestMulTable{ //main method public static void main(String[]args) { //display the table heading System.out.println(“ Multiplication table”); System.out.println(“…………………………………………..”); // display the number title System.out.println(“ | “);

TestMulTable.java

for(int j=1; j<=9; j++) System.out.println(“ “ + j):System.out.println(“ “);

// print table bodyfor(int i =1; i<=9; i++){ for(int j=1;j<=9;j++) { // display the product and align properly if(i*j <10) System.out.print(“ “ +i*j); else System.out.print(“ ”+i*j); }

TestMulTable.java

System.out.println(); } }}

The break Keyword

The continue Keyword

TestBreak.java

//TestBreak.java;test the break keyword//in the looppublic class TestBreak{ // main method public static void main(String[]args) { int sum =0; int item =0;

while(item<5) { item++; sum+= item;

TestBreak.java

if(sum >=6) break; } System.out.println(“The sum is”+ sum); }}

TestContinue.java

//TestContinue.java; test the continue //keywordpublic class TestContinue { public static void main(String[]args) { int sum = 0; int item = 0;

while(item<5) { item++; if(item == 2) continue; sum+=item; }

TestContinue.java

System.out.println(“The sum is “+ sum); }}

PrintPyramid.java//PrintPyramid.java;print a pyramid of numberspublic class PrintPyramid{ public static void main(String[]args) { for(int row = 1;row<6; row++) {

// print leading spaces for(int column =1;column<6-row;column++) System.out.print(“ “); // print leading numbers for(int num=row; num>=1; num--) System.out.print(num);

PrintPyramid.java

//print ending numbers for(int num=2; num<=row; num++) System.out.print(num);

// start a new line System.out.println(); } }}

Methods

public static int max(int num1, int num2){ int result = 0;

if(num1>num2) result = num1; else result = num2;

return result;}

Return value

returnValueType methodName

parameters

modifier

Methodbody

TestMax.java//TestMax.java;

public class TestMax{ public static void main(String[]args) { int i = 5;

int j = 2; int k = max(i,j); System.out.println(“The maximum between “ +i+” and”+j+” is”+k); }

TestMax.java

// a method for finding the max//between two numbers

static int max(int num1, int num2) { if(num1>num2) return num1; else return num2; }}

TestMax.java

void nPrintln(String message, int n){ for( int i=0; i< n; i++) System.out.println(message);}

TestPassByValue.java

//TestPassByValue.javapublic class testPassByValue{ public static void main(String[]args) { // declare and initialise variables int num1 =1; int num2 =2; System.out.println(“Before invoking the swapmethod, num1 is”+num1+”and num2 is”+num2);

TestPassByValue.java

//invoke the swap method to attempt to// swap two variablesswap(num1, num2);System.out.println(“After invoking the swap method, num1 is”+num1+”and num2 is”+num2);

//the method for swapping two variablesstatic void swap(int num1, int num2){ System.out.println(“ inside the swap method”); System.out.println(“ before swapping n1 is”+n1+”n2 is”+ n2);

TestPassByValue.java

//swapping n1 with n2

int temp=n1; n1=n2; n2=temp;

System.out.println(“ After swapping n1 is “+n1+”n2 is”+n2); }}

TestPassByValue.java

2

2

1

n1

n2

temp

1

2

n1

n2

1

2

num1

num2

swap(n1,n2)

swap(num1, num2)

Pass by value

Execute swap

swap

Summary

• Repetitions;

• while loop;

• do loop;

• for loop;

• nested for loop;

• methods;