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Lecture 04

Structural Programming

in C++

You will learn:i) Operators: relational and logicalii) Conditional statementsiii) Repetitive statementsiv) Functions and passing parameterv) Structures

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Structural Programming in C and C++

• Even though object-oriented programming is central to C++, you still need to know basic structural constructs to do the job.

• The implementation of the member functions of a class (i.e. methods in OOP term) is largely structural programming.

• Almost all the structural programming constructs in C are also valid in C++.

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Relational Operators

. . . int n; cout << "Enter a number: "; cin >> n; cout << "n<10 is " << (n < 10) << endl; cout << "n>10 is " << (n > 10) << endl; cout << "n==10 is " << (n == 10) << endl; . . .

A Sample Run:Enter a number: 20 n<10 is 0 n>10 is 1 n==10 is 0

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Relational Operators(cont.)

• Displaying the results of relational operations, or even the values of type bool variables, with cout << yields 0 or 1, not false and true.

• The relational operators in C++ include: >, <, ==, !=, >=, <=.

• Any value other than 0 is considered true, only 0 is false.

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Logical Operators

Logical AND Operator: &&

if ( x == 7 && y == 11 )   statement;

• Logical OR Operator: ||

if ( x < 5 || x 15 ) statement;

Logical NOT Operator: !

if !(x == 7)

statement;

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Operator Precedence

SUM = SUM + 5OR

SUM =+ 5

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Conditional Statement: ifSyntax

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Conditional Statement: if…elseSyntax

If (x > 100) statement;

else statement;

A statement can be a single statement or a compound statement using { }.

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Conditional Statement: switchSyntax

switch(speed) {case 33:

statement;break;

case 45:statement;break;

case 78:statement;break;

}

Int a,b,c; char op;

cin >> a >>op >>b;

switch(op)

case ‘+’:

c= a+b;break;

case ‘-’:

c= a-b;break;

default:

cout <<“unknown operator”;

}

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Conditional OperatorSyntax

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Conditional Operator Syntax

result = (alpha < 77) ? beta : gamma;

is equivalent to

if (alpha < 77)

result = beta;

else

result = gamma;

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Result = (num > 0)?‘positive’: (num<0) ?’negative’: ’zero’

is equivalent to

if num>0

result = ‘positive’;

else

if num <0

result = ‘negative’;

else

result = ‘zero’;

Example

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The for LoopSyntax

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The for LoopControl Flow

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Example

For (I=1;I<=10;I++) For (I=1;I<=10;I++)

cout << I; cout << “*”

cin>>n; For (I=1;I<=10;I++)

For (I=1;I<=n;I++) cout << “*” <<endl;

sum = sum +I;

cout << sum;

For (I=1;I<=3;I++)For (j=1;j<=10;j++)cout << I << “*” <<j<<“=“<<I*j;

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The while LoopSyntax

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The while LoopControl Flow

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Example

i = 1;

While (i<=10)

cout << i;

Cin >> n; I = 1;

While (I<=n)

{ sum = sum + I;

cout << sum

}

While ( I<=10 )

cout << “*”;

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The do LoopSyntax

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The do LoopControl Flow

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Example

Do

{cout <<I;

I = I +1;

} while (I<=10);

Cin >> n;Do{

cout <<I;I ++;

} while (I<=n)

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Functions

Def : Set of statements used for a specific task

Syntax: returntype fName( arguments)

{… statements return variblename}

Types of functions:

1. Function with no arguments and no return

2. Functions with argument and no return

3. Functions with argument and a return

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Using Functions To AidModularity

. . . void starline(); // function prototype

int main() { . . . starline(); . . . starline(); return 0; }

void starline() // function definition{ for(int j=0; j<45; j++) cout << '*'; cout << endl; }

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Passing Arguments To Functions

void repchar(char, int);

int main() { char chin; int nin; cin >> chin; cin >> nin; repchar(chin, nin); return 0; }

void repchar(char ch, int n) { for(int j=0; j < n; j++) cout << ch; cout << endl; }

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Returning Values From Functions

float lbstokg(float);

int main() { float lbs; cout << "Enter your weight in pounds: "; cin >> lbs; cout << "Your weight in kg is " << lbstokg(lbs) << endl; return 0; }

float lbstokg(float pounds) { return 0.453592 * pounds; }

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Using Structures To Group Data

struct part { // declare a structure int modelnumber; // ID# of widget int partnumber; // ID# of widget part float cost; // cost of part };

int main() { part part1; part1.modelnumber = 6244; part1.partnumber = 373; part1.cost = 217.55; cout << "Model " << part1.modelnumber << ", part " << part1.partnumber << ", cost $" << part1.cost << endl; return 0; }

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Structures Within Structures

struct Distance { int feet; float inches; }; struct Room { Distance length; Distance width; };

int main() { Room dining={ {13, 6.5},{10, 0.0} }; float l = dining.length.feet + dining.length.inches/12; float w = dining.width.feet + dining.width.inches/12; cout << "Dining room area is " << l * w << " square feet" << endl; return 0; }