ALGORITHMS
- A procedure for solving a problem in terms of the actions to be executed, and the order in which these actions are to be executed, is called an algorithm.


PROGRAM CONTROL
- Specifying the order in which statements are to be executed in a computer program is called program control.


Pseudocode
- Pseudocode is an artificial and informal language that helps programmers develop algorithms. It helps the programmer "think out" a program before attempting to write it in a programming language.


CONTROL STRUCTURES
- Usually statements in a program are executed one after another in the order in which they are written. This is called sequential execution. However, some C++ statements could be written that enable the programmer to specify that the next statement to be executed may be other than the next one in sequence. This is called transfer of control- reminds the notorious "goto" statements of the past.


- All programs could be written in terms of only three control structures:
Sequence structure, [DEFAULT in C++]
Selection structure, [USE OF 'if', 'if/else', 'switch'] and
Repetition structure. [USE OF 'while', 'do/while','for']


FLOW CHART
- A flow chart is a graphical representation of an algorithm or of a portion of an algorithm. Flowcharts are drawn using certain special-purpose symbols such as rectangles, diamonds, ovals, and small circles connected by arrows called flowlines.


Usual meaning of flowchart symbols:


-OVAL - one containing the word "Begin" and the other containing the word "End"
- These are the usual first and last symbols of a flowchart.


-RECTANGLE - action symbol
-indicates an action to be taken like a calculation etc.


-DIAMOND - decision symbol
-indicates a decision is to be made.


C++ KEY WORDS
- keywords are words reserved by the language to implement various features and are those that should not be used as identifiers such as for variable names.


The following are C++ keywords:


asm, auto, break, bool, case, char, catch, class, const, const_cast, continue, delete, default, do, double, dynamic_cast, else, enum, explicit, extern, false, float, for, friend, goto, if, inline, int, long, mutable, namespace, new, operator, private, protected, public, register, reinterpret_cast, return, short, signed, sizeof, static, static_cast, struct, switch, template, this, throw, true, try, typedef, typeid, typename, union, unsigned, using, virtual, void, volatile, wchar_t, while.


THE if SELECTION PROCEDURE


- A selection structure is used to choose among alternative courses of action.


Example:


Pseudocode
If students's grade is greater than or equal to 60
Print "Passed".


C++ statement


if ( grade >= 60)

	cout << "Passed";

if LOGIC - condition true - statement executed, condition false - statement ignored and control is passed to the next statement.


In C++ draft standard, the keywords "true" and "false" are used to represent the values of type "bool" - based on the word boolean algebra.


if STRUCTURE - single-entry/single-exit structure.


THE if/else SELECTION STRUCTURE


- A different action is to be performed when the condition is "true" than when the condition is "false".


Example:


Pseudocode:
If student's grade is greater than or equal to 60
Print "Passed"
else
Print "Failed".


C++ statement


if ( grade >= 60 )

	cout << "Passed";

else

	cout << "Failed";

C++ provides the conditional operator (?:) that is closely related to the if/else structure.


The conditional operator is C++'s only ternary operator - it takes three operands.


Example:
cout << ( grade >= 60 ? "Passed" : "Failed" );

This could also be written as:
grade >= 60 ? cout << "Passed" : cout << "Failed";


Nested if/else structure


Pseudocode:


If student's grade is greater than or equal to 90

	Print "A"

else

	If student's grade is greater than or equal to 80

	Print "B"

else

	If student's grade is greater than or equal to 70

	Print "C"

else

	If student's grade is greater than or equal to 60

	Print "D"

else

	Print "F".

C++ statement


if ( grade >= 90 )

	cout << "A";

else

	if ( grade >= 80 )

		cout << "B";

	else

		if ( grade >= 70 )

			cout << "C";

		else

			if ( grade >= 60 )

				cout << "D";

			else

				cout << "F";

This is the same as:


if ( grade >= 90 )

	cout << "A";

else if ( grade >= 80 )

	cout << "B";

else if ( grade >= 70 )

	cout << "C";

else if ( grade >= 60 )

	cout << "D";

else

	cout << "F";

This latter form is popular because it avoids the deep indentation of the code to the right.


Compound statement


if ( grade >= 60 )

	cout << "Passed.\n";

else

{

	cout << "Failed.\n";

	cout << "You must take this course again.\n";

}

The braces surrounding the two statements are important, without them, the statement


cout << "You must take this course again.\n";


would be outside the body of the "else" part of the "if", and would execute regardless of whether the grade is less than 60.


THE while REPETITION STRUCTURE


- Allows the programmer to specify that an action is to be repeated while some condition remains true.


Example:


Pseudocode
While the power of 2 is not larger than 1000
keep on getting the values of the power of 2.


C++ statement


int product = 2;

while ( product <= 1000 )

product = 2 * product;

The initial value of "product" here which is 2 and which is obtained by raising the power of 2 by 1 is called INITIALIZATION.


A PROBLEM


A class of ten students took a quiz. The grades (integers in the range of 0 to 100) for this quiz are availabale to you. Determine the class average on the quiz.


Pseudocode
Set total equal to zero
Set grade counter to one


While grade counter is less than or equal to ten
Input the next grade
Add the grade into the total
Add one to the grade counter


Set the class average to the total divided by ten
Print the class average


C++ program


// Class average program with counter controlled repetition.

# include <iostream.h>


int main()

{

	int total,		// sum of grades

		gradeCounter,	// number of grades entered

		grade;		// one grade

	float	average;	// average of grades


	// initialization phase

	total = 0;		// Clear total

	gradeCounter = 1;	// prepare to loop


	// processing phase
	while ( gradeCounter <= 10) {	// loop 10 times

	cout << "Enter grade: ";	// prompt for input

	cin >> grade;			// input grade

	total = total + grade;		// add grade to total

	gradeCounter = gradeCounter + 1; // increment counter

}


	// termination phase

	average = total / 10.0;		// division

	cout << "Class average is " << average << endl;


	return 0;	//indicate program ended successfully

}

Counter variables are normally initialized to zero or one, depending on their use.


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AFTER TODAY'S CLASS IS OVER, LOOK AT THE ASSIGNMENT.