Software Development Method

• Specify the problem.

• Analyze the problem.

• Design the algorithm to solve the problem.

• Implement the algorithm.

• Test and verify the completed problem.

• Maintain and update the problem.

Problem• We need to state the problem clearly and

unambiguously.

• It helps get a clear understanding of what is required for its solution.

• Eliminate unimportant aspects and concentrate on the root problem.

• We might need more information.

• Example: Write a program to calculate the number of calories in a cheese sandwich

Implementation

• Write the algorithm as a C++ program.• First tell the C++ compiler about the problem

data requirements. - What memory cell names you are using. - What kind of data will be stored in each

memory cell.• Next, convert each algorithm step into one or

more C ++statements.

Testing

• Verify the completed program that it works.

• Run the program several times using different sets of data.

• Make sure it works properly in each case.

• In this example, enter a few more test values of BREAD, CHEESE, MAYONNAISE, and PICKLES.

Maintenance• Maintaining and updating the program may be necessary

to correct previously undetected program errors or to comply with external changes in requirements.

• External (manuals) and internal (comments) documentation is necessary.

• Good programming style guidelines must be followed so that others, even the original programmer, may be able to read the program in the future.

• Keep it up-to-date.• 85% of total cost is spent for software maintenance.

A program written in C++ 1 // This program calculates the number calories in a cheese sandwich

2 #include <iostream.h>

3 const int BREAD = 63;

4 const int CHEESE = 106;

5 const int MAYONNAISE = 49;

6 const int PICKLES = 25;

7 int main()

8 {

9 int totalCalories;

10 totalCalories = 2 * BREAD + CHEESE + MAYONNAISE + PICKLES;

11 cout << "There were " << totalCalories;

12 cout << " calories in my lunch yesterday."<< endl;

13 return 0;

14 }

Comments• Line 1 is called comment.

• It tells the reader what the program is going to to.

• Line 1 is ignored by the compiler.

• Comment begins with a double slash (//).

• It extends to the end of the line.

• Another way of comments:Insert your comment between /* and */We can write any number of lines.

Preprocessor directives• Line 2 is a directive to the C++ preprocessor.• Commands that give instructions to the C ++

preprocessor.• C++ preprocessor modifies the text of a C ++

program before it is compiled.• Begins with a number symbol (#) as its 1st

nonblank character.• #include directive instructs the preprocessor to

insert definitions from a standard header file (iostream.h) into a program before compilation.

• This file includes constant, variable, and function declarations needed by the program.

A constant declaration

• Line 3 through 6 instruct the compiler to assign the identifier on the left of the equal

sign a place in memory and to store the value on the right of equal sign in

that place.

• Generally, programmers use all uppercase for constant identifiers.

Function main• Program execution begins at main function.• Every C ++ program has a main function.• The body of a function is enclosed in braces {, }.• A function body has two parts: declaration and

executable statements.• Declarations tell the compiler what memory cells

are needed in the function (totalCalories).• Executable statements are translated into machine

languages before execution.• Main function returns an integer and takes nothing

as an argument (not always).

Reserved Words

• int, void, const are all reserved words

• Appears in lower case.

• Have special meaning in C++.

• Can’t be use for other purposes.

Standard Identifiers

• Have special meaning in C++.

• Standard identifiers cout and cin are names of operations defined in the standard input/output library.

• Can be redefined and used by the programmer for other purposes.

User-Defined Identifiers• Used to name memory cells that will hold data

and program results.• Used to name operations that we define.• The first user-defined identifier is BREAD.• Syntax rules: 1. An identifier must consist only of letters,

digits, and underscores. 2. An identifier cannot begin with a digit. 3. A C++ reserved word cannot be used as

an identifier. 4. An identifier defined in a C++ standard

library should not be redefined.

Uppercase and Lowercase Letters

• Uppercase and lowercase letters are considered different by the C++ compiler.

• xyz, Xyz and XYZ are all different variables. • Normally, standard library functions use all

lowercase letters, while macros use all uppercase chars.

• Programmers should use upper and lowercase letters consistently.

Variable declaration• Variable : Memory cell used to store a

program’s input data and its computational results.

• Variable declaration: Statement that tells the compiler the names of the variables and the type of data stored in each variable.

Example :

int totalCalories;

Gives the name of a variable (total Calories) used to store an intege number.

Methods of variable creation

• Global variable– declared very early stage– available at all times from anywhere– created at the start of the program, and lasts

until the end, it is taking up lots of memory– difficult to debug

Methods of variable creation (continued)

• Local on the fly variables– simply created when they are needed, – only available from within the routine in which

they were created– memory requirement is less– easy to debug

Methods of variable creation (continued)

• Local defined variable– created before they are needed – only available in the routine in which they were

created.– Memory requirement is less– easy to debug– the most usually favored method

Data Types

• data type: set of values and a set of operations on those values.

• A standard data type in C++:

char double or float int(Real numbers) (Integers)(A letter, digit,

or a special symbol)

Data Types In C++ every variable has a type which determines: - A set of values the variable can take (range of the

data type). - A set of operations allowed. - Number of bytes used to represent the variable in

the memory cells.

Example of predefined data type in C: int => integer, range: -32767 ~ 32767; Example: -5, 0, 32767; occupy two bytes/four bytes.

Data Types Example of predefined data type in C++:• float => real number, range: at least 6 decimal

digits (4 bytes). Example: -12.8, 0.0, 6.9. • double => real number (double precision), range:

15 decimal digits of precision (8 bytes).• char => character, occupy one byte. Data type char represents an individual character

value: a letter, a digit, or a special symbol. A character value must be enclosed in single quotes.

Example: 'A' 'b' '2' '%' .

cin and cout

• Data can be placed in memory by assignment or by copying from input devices.

• Input operations transfer data from external sources into the computer.

• Output operations display the results of the program to the computer user.

• Input and output functions in <iostream.h> include cin(input) & cout (output).

• Function calls are used to call or activate these input and output functions.

Programs in MemoryMemory before execution Memory after execution

Machine language calculate calories

program

63

?

memory

BREAD

totalCalories

106

CHEESE

49

MAYONNAISE

25

PICKLE

Machine language calculate calories

program

63

306

memory

BREAD

totalCalories

106

CHEESE

49

MAYONNAISE

25

PICKLE

The return Statement

return (0)

Transfer control from your programto the operating system at the end of the main section, or from a function back to its activator.

0 is the result of function main’sexecution, it indicates that your program executed without error.

Comments in Programs

Comments in programs help others read and understand the programs.

Compiler ignores comments.

They are not translated into machine language

Program Style

• Use structured programming methodology (top-down design).

• Your program must be readable.• Use meaningful variable names and function

names.• Indent your program properly.• A program should be well documented so that

others can read, use, and modify it easily.

Program Style

• Anticipate errors.

• Don’t use goto.

• Use functions extensively

• Avoid global variables and side effects.

• Test your programs as you build it - bottom up testing.

Structured Programming

• Design your program in a top down manner.• Always decompose your problem into

simpler subproblems.• Constructs used for decomposition– Sequence– Selection– Iteration

Decomposition (First round)

• a) Sleep as late as possible.

• b) Get dresses.

• c) If you want breakfast then have breakfast.

• d) Drive to the university.

Sequence: Do steps one after the other.

Step a is followed by step b followed by step c etc.

Selection: If <condition> then do something

or If <condition> then do something1 else do something2.

Problem - Get ready for school

Expansion of step a

While alarm not ringing

Sleep

Iteration: Carry out step(s) a number of times.

Your program must be readableA program should have• A good structure and design.• A good choice of identifiers.• Good indentation and use of blank lines.• Good documentation.• Avoid “clever” programming tricks that – save a little computer time.– make you feel that you are “smart”.– reduce some lines of codeHuman time is the most important resource.

Indent your program properly

• Enhance readability.

• Easy to identify the program’s modules.

• Use blank lines to offset each function.

• Use blank lines to separate individual blocks of code visibly.

How to handle an error?

• Display error message and turn error flag on.

• Possible actions:

– Ignore erroneous data and continue.

– Give warning message.

– Terminate the program.

– Use a diagnostic mode and normal mode of program execution.

Modular programming• Always use the divide and conquer

approach.

• Use functions whenever you identify a clearly distinct task during your process of structures program development.

• A function should avoid global variable.

• A good rule of thumb is to limit each function (including main) to 1 page in length.

% Operation

• 4 % 5 = 4

• 7 % 7 = 0

• 7 % 6 = 1

• 28 % 4 = 0

• 16 % -5 varies

• 16 % 0 undefined

In C++, an additional arithmetic operator, the % (remainder operator) is used with integer operands to find the remainderof integer division.

The % operator requires that both operands be of type int.

Integer Division

• 4 / 16 = 0

• 16 / 4 = 4

• 17 / 4 = 4

• 16 / -3 varies

• 0 / 5 = 0

• 16 / 0 = undefined

When applied to two positive integers, the result of the division must be an integerin C++, the remainder is thrown away.

Increment & Decrement Operators• ++ unary increment operator.• -- unary decrement operator.• If a variable x incremented by 1, you can use x++

rather than x = x + 1 or x += 1.• If a variable x decremented by 1, you can use x--

rather than x = x - 1 or x -= 1.• Preincrement operator ++x.• Postincrement operator x++.• Predecrement operator --x.• Postdecrement operator x--.• What is the difference between preincrementing

and postincrementing?

Preincrementing & Postincrementing #include <iostream.h> main() { int x; x = 5; cout << x << endl; cout << x++ << endl; // post increment cout << x << endl << endl;

x = 5; cout << x << endl; cout << ++x < endl; // preincrement cout << x < endl;

return (0); // successful termination }

556

566

Output

Arithmetic Expression• Arithmetic expressions are used to manipulate type int and

double data. • e.g. n1 + n2 • In C++, an expression is composed of terms and operators.

A term, such as n1 and n2, represents a single data value, which must be one of the following:

- a constant - a variable - a function call - an expression in parentheses • Four arithmetic operators that apply to all numeric data

types are: + (addition), - (subtraction), * (multiplication), and / (division).

Arithmetic Expressions Rules

• Parentheses rules– All expressions in parentheses must be evaluated first. In

nested parenthesized expressions, the innermost expression evaluated first.

• Precedence rules for arithmetic operators Operators in the same expression are evaluated in the

following order: – unary +, - first.

– Multiplication (*), division (/), and mode(%) next.

– Addition (+) and subtraction (-) last.

Arithmetic Expressions Rules

• Associativity rules• Unary operators in the same subexpression and at the same

precedence level (such as + and -) are evaluated right to left (right associativity). Binary operators in the same subexpression and at the same precedence level (such as + and -) are evaluated left to right (left associativity).

• Type rules– If both operands are integers -> result is integer.

– If any of the operands is floating point -> result is floating.

Assignment statement X = expression

• If LHS and RHS are both same type -> no conversion.

• If LHS is floating and RHS is integer -> RHS converted to floating.

• If LHS is integer and RHS is floating -> RHS truncated to integer.

• The value of an assignment statement is the value assigned -> X = RHS value

Assignment statement• Problem: What will be printed by the following

program fragment?

int x = 2, y = 5, z = 3, p, q, r; float a; p = (x + y * z) * 5 +3/5 * 5; r = q = 3.0/5 * 5; a = (5 - 3) / 3; cout << p << endl; cout << q << endl; cout << a << endl;

Assignment statement

P = (x +y * z) * 5 + 3 /5 *5

= (2 + 15) * 5 +3 /5 * 5

= 17 *5 + 3 / 5 *5

= 85 + 3 / 5 * 5

= 85 + 0 * 5

= 85 + 0

= 852 5 3 85

x y z p

Mathematical Formula & C Expression

a = r 2

Mathematical Formula C Expression

a = PI * r * r

x - am =

y - b m = (y - b) / (x - a)

r1 = -b + b 2 - 4ac

2ax = pow (b, 2) - 4 * a * c ;

r1 = (- b + sqrt ( x)) / (2 * a);

Interactive Mode, Batch Mode, and Data Files

• In interactive mode, the user types in data during the execution of the program.

• Prompts are included so that the user knows exactly when to enter each data item.

• Batch mode scans input data from a file prepared prior to program execution.

• Input can be redirected to a file by using < (left angle) command.

• For example, myprog < mydata causes myprog to take input data from file mydata.

Interactive Mode, Batch Mode, and Data Files

• To convert interactive version of miles-to-kilometers program to batch, each preceding prompt statement is replaced by an echo print following scanf line.

• Program output can also be redirected to a disk file instead of the screen.

• For example, metric > myoutput command causes to write the output to file myoutput.

• UNIX or MS-DOS uses the > (right angle) command to redirect output to a file.

• These forms of input/output redirection are done via the operating system.

Common Programming Errors

Bugs: Errors in programs are called.

Debugging: process of correcting errors in program.

Errors

Syntax errorsRun-time errors

Logic errors

Undetected errors

Syntax Errors• Occurs when your code violates one or more

grammar rules of C++.• Detected by the compiler as it attempts to

translate.• If error occurs, program cannot be translated

and program will not be executed.• Example:

– Missing semicolon at the end of a statement.– Undeclared variables– Omit to put a quotation mark.

Run-Time Errors

• Detected and displayed during the execution.

• Occurs when the program directs the computer to perform an illegal operation.

• If errors occur, the computer will stop executing your program.

• Example:

– divide by zero error

– pointer error.

Undetected Errors

• Undetected errors do not prevent a C++ program from running to completion.

• However, may lead to incorrect results. These can be discovered by thorough testing.

• Examples of undetected errors are

- mixing character and numeric data

- transposing variables, etc.

Logic Errors

• Occur when a program follows a faulty algorithm.

• Do not display error message.• Very difficult to detect.• Only sign of a logic error can be unexpected

results.• It can be detected by comparing its output to

calculated results.

• Well-written programs contain comments that explain in English what the program is doing.

• Most programs use libraries that provide tools the programmer need not recreate from scratch.

• By adding a #include line that specifies a header file(such as iostream.h, math.h), you gain access to libraries.

• Every complete C++ program contains a function main. When we run the program, the statements in the body of main are executed in order.

Overview

Overview• Most programs are composed of the following

three phases: input =>computation =>output • Use cin to accept input typed by the user, cout to

display messages and data values on the screen. • Data values come in many different types, each of

which is defined by a domain and a set of operations.

• Variables have three attributes: a name, a value, and a type. All variables used in a C++ program must be declared first.

• The order of operations in an expression is determined by rules of precedence.