5.pptx fundamental programing one branch

1
Abraham H.
Fundamentals of Programming I
Control Statements

2
Outline
 Introduction
 Conditional structure
 If and else
 The Selective Structure: Switch
 Iteration structures (loops)
 The while loop
 The do-while loop
 The for loop
 Jump statements
 The break statement
 The continue statement

3
Introduction
 C++ provides different forms of statements for different
purposes
 Declaration statements
 Assignment-like statements. etc
 The order in which statements are executed is called flow
control
 Branching statements
 specify alternate paths of execution, depending on the
outcome of a logical condition
 Loop statements
 specify computations, which need to be repeated until a
certain logical condition is satisfied.

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Branching Mechanisms
 if-else statements
 Choice of two alternate statements based on condition
expression
 Example:
if (hrs > 40)
grossPay = rate*40 + 1.5*rate*(hrs-40);
else
grossPay = rate*hrs;
 if-else Statement syntax:
if (<boolean_expression>)
<yes_statement>
else
<no_statement>
 Note each alternative is only ONE statement!
 To have multiple statements execute in either branch  use
compound statement {}

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Compound/Block Statement
 Only "get" one statement per branch
 Must use compound statement{}for multiples
 Also called a "block" statement
 Each block should have block statement
 Even if just one statement
 Enhances readability
if (myScore > yourScore)
{
cout << "I win!n";
Sum= Sum + 100;
}
else
{
cout << "I wish these were golf scores.n";
Sum= 0;
}

6
The Optional else
 else clause is optional
 If, in the false branch (else), you want "nothing" to
happen, leave it out
 Example:
if (sales >= minimum)
salary = salary + bonus;
cout << "Salary = %" << salary;
 Note: nothing to do for false condition, so there is no else
clause!
 Execution continues with cout statement

7
Nested Statements
 if-else statements contain smaller statements
 Compound or simple statements (we’ve seen)
 Can also contain any statement at all, including another if-
else stmt!
 Example:
if (speed > 55)
if (speed > 80)
cout << "You’re really speeding!";
else
cout << "You’re speeding.";
 Note proper indenting!

8
Multiway if-else: Display
 Not new, just different indenting
 Avoids "excessive" indenting
 Syntax:

9
Multiway if-else Example: Display

10
The switch Statement
 A new statement for controlling multiple branches
 Uses controlling expression which returns bool data type (T or
F)
 Syntax:

11
The switch Statement : Example

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The switch: multiple case labels
 Execution "falls thru" until break
 switch provides a "point of entry"
 Example:
case "A":
case "a":
cout << "Excellent: you got an "A"!n";
break;
case "B":
case "b":
cout << "Good: you got a "B"!n";
break;
 Note: multiple labels provide same "entry"

13
switch Pitfalls/Tip
 Forgetting the break;
 No compiler error
 Execution simply "falls thru" other cases until break;
 Biggest use: MENUs
 Provides clearer "big-picture" view
 Shows menu structure effectively
 Each branch is one menu choice

14
switch and If-Else
switch example if-else equivalent
switch(x)
{
case 1:
cout<<"x is 1";
break;
case 2:
cout<<"x is 2";
break;
default:
cout<<"value of x unknown";
}
if(x == 1)
{
cout<<"x is 1";
}
else if(x == 2)
{
cout<<"x is 2";
}
else
{
cout<<"value of x unknown";
}

15
Iteration Structures (Loops)
 3 Types of loops in C++
 while
 Most flexible
 No "restrictions"
 do -while
 Least flexible
 Always executes loop body at least once
 for
 Natural "counting" loop

16
while Loops Syntax
// custom countdown using while
#include<iostream.h>
void main()
{
int n;
cout<<"Enter the starting number:";
cin>>n;
while(n>0)
{
cout<<n<<", ";
--n;
}
cout<<"FIRE!n";
}
Output:
Enter the starting number: 8
8, 7, 6, 5, 4, 3, 2, 1, FIRE!

17
do-while Loop Syntax
//number echoer
#include <iostream.h>
void main()
{
long n;
do{
cout<<"Enter number (0 to end): ";
cin>>n;
cout<<"You entered: " << n << "n";
}while(n != 0);
}
Output:
Enter number (0 to end): 12345
You entered: 12345
You entered: 160277
You entered: 0

18
While vs. do-while
 Very similar, but…
 One important difference
 Issue is "WHEN" boolean expression is checked
 while: checks BEFORE body is executed
 do-while: checked AFTER body is executed
 After this difference, they’re essentially identical!
 while is more common, due to it’s ultimate "flexibility"

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for Loop Syntax
for (Init_Action; Bool_Exp; Update_Action)
Body_Statement
 Like if-else, Body_Statement can be a block statement
 Much more typical
// countdown using a for loop
#include <iostream.h>
void main ()
{
for(int n=10; n>0; n--)
{
cout<< n << ", ";
}
cout<< "FIRE!n";
}
Output:
10, 9, 8, 7, 6, 5, 4, 3, 2, 1, FIRE!

20
Converting Between For and While Loops
for (int i = 1; i < 1024; i *= 2){
cout << i << endl;
}
int i = 1;
while (i < 1024) {
cout << i << endl;
i *= 2;
}

21
Loop Pitfalls: Misplaced ;
 Watch the misplaced ; (semicolon)
 Example:
while (response != 0) ;
{
cout << "Enter val: ";
cin >> response;
}
 Notice the ";" after the while condition!
 Result here: INFINITE LOOP!

22
Loop Pitfalls: Infinite Loops
 Loop condition must evaluate to false at some iteration through
loop
 If not  infinite loop.
 Example:
while (1)
{
cout << "Hello ";
}
 A perfectly legal C++ loop  always infinite!
 Infinite loops can be desirable
 e.g., "Embedded Systems"

23
JUMP Statements -The break and continue Statements
 Flow of Control
 Recall how loops provide "graceful" and clear flow of
control in and out
 In RARE instances, can alter natural flow
 break;
 Forces loop to exit immediately.
 continue;
 Skips rest of loop body
 These statements violate natural flow
 Only used when absolutely necessary!

24
 Break loop Example
// break loop example
void main()
{
int n;
for(n=10; n>0; n--)
{
cout<<n<<", ";
if(n==3)
{
cout<<"countdown aborted!";
break;
}
}
}
Output:
10, 9, 8, 7, 6, 5, 4, 3, countdown aborted!

25
 Continue loop Example
// continue loop example
void main ()
{
for(int n=10; n>0; n--)
{
if(n==5)
continue;
cout<<n<<", ";
}
cout<<"FIRE!n";
}
Output:
10, 9, 8, 7, 6, 4, 3, 2, 1, FIRE!

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Nested Loops
 Recall: ANY valid C++ statements can be
inside body of loop
 This includes additional loop statements!
 Called "nested loops"
 Requires careful indenting:
for (outer=0; outer<5; outer++)
for (inner=7; inner>2; inner--)
cout << outer << inner;
 Notice no { } since each body is one statement
 Good style dictates we use { } anyway

5.pptx fundamental programing one branch

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