Download Introduction to Programming G50PRO University of Nottingham Unit

Introduction to Programming
G50PRO
University of Nottingham
Unit 6 : Control Flow Statements 2
Paul Tennent
http://paultennent.wordpress.com/G50PRO.html
[email protected]
Room C7
Control Flow Statements

The statements inside your source files are
generally executed from top to bottom

Control flow statements, break up the flow of
execution by employing decision making,
looping, and branching
Control Flow Statements

Decision-making statements




Looping statements




if-then
if-then-else
switch
for
While
do-while
Branching statements



break
continue
return
Why Looping?

To automate the repetition of instructions.

To iterate through data and test for certain
condition

To keep attempting for some operation
(such as obtaining data from a remote
computer over a network)
Loops: for Statement


for statement provides a compact way to iterate over a range of
values.
Repeatedly loops until a particular condition is satisfied. The general
form of the for statement can be expressed as follows:
for (initialization; Condition; increment) {
statement(s)
}

keep in mind that:

initialization expression initializes the loop; it's executed once, as the loop
begins.

When the Condition is checked before each iteration through the loop. When it
evaluates to false, the loop terminates.

increment expression is invoked after each iteration through the loop; it is
perfectly acceptable for this expression to increment or decrement a value.
Loops: for Statement
1
for (int i=0; i<2; i++){
Initialization
Statement (s);
8
}
2
5
Condition
Evaluation
true
3
6
Statement (s)
4
7
Increment
ii =
0
=2
1
false
for Statement
class ForCount {
public static void main(String[] args){
for(int i=1; i<5; i++){
System.out.println("Count is: " + i);
}
}
}

The output of this program is:




Count is: 1
Count is: 2
Count is: 3
Count is: 4
while Statement

The while statement continually executes a block of
statements while a particular condition is true.
while (expression) {
statement(s)
}


The expression must return a boolean value
The while statement continues testing the
expression and executing its block until the
expression evaluates to false
while Statement
boolean found = false;
while (!found) {
//code to search for a value in list
//set found = true to exit
}
Condition
Evaluation
true

The statement(s) is executed over and
over until the condition becomes false

statement(s) is executed Zero or more
times
Statement (s)
false
while Statement
class Count {
public static void main(String[] args){
int count = 1;
while (count < 5) {
System.out.println("Count is: " + count);
count++;
}
System.out.println(“Outside while loop");
}//main end
}//class end

The output of this program is:





Count is: 1
Count is: 2
Count is: 3
Count is: 4
Outside while loop
do-while Statement

The while statement continually executes a block of
statements while a particular condition is true.
do {
statement(s)
}while (expression)

The expression must return a boolean value

do-while evaluates its expression at the bottom of
the loop instead of the top. Therefore, the
statements within the do block are always executed
at least once
do-while Statement
Statement (s)
boolean exit
= false;
do {
statement(s)
//set exit = true to exit
} while (!exit);

The statement(s) is executed over and
over until the condition becomes false

statement(s) is executed at least once
true
Condition
Evaluation
false
do-while Statement
class Count {
public static void main(String[] args){
int count = 10;
do{
System.out.println("Count is: " + count);
count++;
} while (count < 5)
System.out.println(“Outside while loop");
}//main end
}//class end

The output of this program is:


Count is: 10
Outside while loop
Infinite Loops

infinite loop, will execute until the user
interrupts the program.

This is a common type of logical error.
always double check your loop condition.
for(int i = 2; i > 1; i++){
System.out.println("Count is: " + i);
}
Notes

If what you really want is to execute the loop 10 times, write the
condition
 Number < 10 and not as Number <= 9

In general, specific values such as "10" should not appear within
the body of your program. You should declare them as finals at
the top of the program
 static final int COUNT = 10;

In Java generally you would more likely want to loop not
from 1 to 10, but from 0 to 9.
All counting in Java tends to start at zero rather than one.
Course Work 2.1 Notes


11 marks for correct execution and meeting
all requirements
4 marks on the Quality of your code

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Follow a logical Structure
Define local Variables at the start of main method
Use constants when needed
Correct indentation
Good use of comments
Summary


Control Flow Statements
Looping statements



for
While
do-while