GAME102 - INTROWHILE LOOPS

G. MacKay

Fundamental Control Structures STRAIGHT LINE

CONDITIONAL

LOOPS

What is LOOP?

Logic that repeats itself

Usually verbally identified by “while” or “until”

In human terms?

while (the light is red) wait

while the meat is raw cook

Flowchart of a WHILE LOOP

Note

ONE ENTRANCE

ONE EXIT

from structure

C++ Code of a WHILE LOOP As follows

while (test) statement;

C++ Code for Counter

As follows

count = 1;while (count<=10){ cout << count<< endl; count = count +1;}

C++ Code for Counter

As follows

count = 1;while (count<=10){ cout << count<< endl; count = count +1;}

NOTE:

initialize count BEFORE LOOP

INCREMENT count INSIDE loop

TEST FOR COUNT

C++ Code for Counter

As follows

count = 1;while (count<=10){ cout << count<< endl; count = count +1;}

LOOP RULE Test should make

progress towards completion

WATCH FOR Incorrect test

direction No increment

C++ Code for Counter – ++ As follows

count = 1;while (count<=10){ cout << count<< endl; count ++;}

Operator ++

Means add one to the variable

count = count + 1;count ++;// SAME!!!

C++ Code for Counter - PROBLEM As follows

count = 1;while (count<=10) cout << count<< endl; count = count +1;

What happens? There are no

braces, so ONE statement goes with the while

Increment is OUTSIDE the while

INFINITE LOOP!!!!!

C++ Code for Counter - PROBLEM As follows

count = 1;while (count>=10){ cout << count<< endl; count = count +1;}

What happens? The test direction

is incorrect

When count=1, test is FALSE so the loop is not entered!!!

C++ Code for Counter – by twos As follows

count = 1;while (count<=10){ cout << count<< endl; count = count +2;}

What happens? When count=1, test

is TRUE so the loop is entered.

Display 1 Count becomes 3…

and Display 3 Then.. 5, 7, 9 EXIT… (on 11)

C++ Code for Counter – by twos As follows

count = 1;while (count<=10){ cout << count<< endl; count += 2;}

Operator +=

Means add whatever is on the right side to whatever is on the left side

count = count + 2;count += 2;// SAME!!!

PROBLEM using loops

Add 10 numberstogether and display the sum

Requirements?

Read 10 numbers Add the numbers Display sum

Design

Flowchart

Design

Pseudo-codePrompt userSet count to 1Set sum to 0While count <=10 Read number Add number to sum Add to 1 to countDisplay sum

CODING #include <iostream>

using namespace std;

int main(){ int number; int sum; int count;

cout << "Enter 10 integer numbers: "; count = 1; sum = 0; while ( count <= 10) { cin >> number; sum += number; count++; } cout << "Sum is " << sum << endl; return 0;}

Testing your code?

Identify the limits of your code Maximum number of reads Minimum number of reads Illegal reads High values entered Low values entered

Test NORMAL case ANDlimits

Testing your code?

In large projects, test groups actually plan tests around the REQUIREMENTS of the project

Testing does not work?

LOGIC ERROR Check that code matches

design FIX code

Check the design is correct FIX design

The OTHER loop…..

do{ statement1; statement2;} while(test);

DO…WHILE Design Difference

PROCESS BLOCK is ALWAYS PERFORMED AT LEAST ONCE

DO…WHILE Design Usage

Do you want to play again?

MAJOR USAGE

DO…WHILE Design Usage

Studies have shown that 90% of all programming loops are WHILE type rather than DO…WHILE

Use DO…WHILE only when it makes sense