Abu Said Md.

Rezoun
Lecturer, Dept. of CSE
Sonargaon University
E-mail: abusaid.rezoun@gmail.com
Contact: 01788210077
 Structure of C Programming
 Component in a program code
◦ Preprocessor Directives / Library
◦ Reserved Word
◦ Data Type
◦ Identifiers and their declarations
◦ Comments
◦ Escape Characters
◦ Operators
◦ Preprocessor Functions
 Good Programming Style
Preprocessor
Directives
Reserved Word

Data Type

Identifiers

Comments
Escape
Character

Operators

Preprocessor
Functions /
statements
 In C programming, the preprocessor
directives start with #include
 It is the specific line to tells the preprocessor
to include the contents of the predefined
function in to the program from the header
file
 The header file contains information and
declarations used by the compiler when
compiling the predefined functions
 Each header file consists of specific function
to be applied
 Examples:
Header File Explanation
<stdio.h> Contains functions prototypes for the
standard input output library function
and the information to use them
<stdlib.h> Contains function prototypes for
conversions of numbers to text and
text to numbers, memory allocation,
random number, and other utility
functions
<string.h> Contains function prototypes for string
processing functions
<time.h> Contains function prototypes and
types for manipulating the time and
date
<math.h> Contains function prototypes for math
library functions
- identify language entities, such as
statements, data types, and language element
attributes;
- They have special meaning to compiler, must
appear in correct location in program, typed
correctly, and used in correct context.
- Case sensitive: differentiates between
lowercase & uppercase letter.
- Example: const, double, int, return
 A data type is a set of data values and a set of operations on those
values.
 Usually has two classes of data types:
◦ Built-in data types
◦ Programmer-defined data types (covered in Structures)
 In addition, the C language has two classes of built-in data types:
◦ Fundamental data types:
 corresponds to the most common, fundamental storage units of a
computer and the most common, fundamental ways of using such
data.
 Example: int, char, double, float, void
 Some of these data types have short, long, signed, and unsigned
variants.

◦ Derived data types:

 Derived from fundamental and programmer-defined data types
using some operators.
 Examples: arrays, strings and structures.
 Int
- is used to declare numeric program
variables of integer type.
- Example:
◦ int counter;
Description:
- declares the program variable counter as an
integer variable.
- We can store only positive or negative integers in
the range –32768 until 32767.
- We can perform arithmetic & assignment
operations on the variable counter
 Char
- is used to declare character variables.
- Example:
 char myCharacter;
Description:
- declares the variable myCharacter to be type
character.
- Character variable stores any printable or
nonprintable character in the computer’s
character set, including lowercase, uppercase
letters, decimal digits, special characters, and
escape sequences.
- Such characters are represented in one byte (8
bits) of the computer’s memory.
 double
- is used to declare a floating-point variables.
- Example:
 double gross_income;
Description:
- declares the program variable gross_income as a
double variable.
- We can store floating-point values in the computer’s
memory.
 Data Type Size (in Byte)

short 2
unsigned short 2

int 4

unsigned int 4

long 4

unsigned long 4

 Unsigned means the number is always zero or

positive, never negative.
 Signed means the number may be negative or
positive (or zero).
 If you don’t specify signed or unsigned, the data type
is presumed to be signed. Thus, signed short and
short are the same.
 Also known as “variables”
 Words to represent and reference certain
program entities
 Refer to a location in memory where value
can be stored.
 Case sensitive: differentiates between
lowercase & uppercase letter.
 Example: student_id, name, Item15,
number_of_strings
 Rules for constructing Identifiers
◦ Identifiers can consist of the capital letters A to Z, the
lowercase letters a to Z, the digits 0 to 9, and the
underscore character _.
◦ The first character must be a letter or an underscore.
◦ There is virtually no length limitation. However, in many
implementations of the C language, the compilers
recognize only the first characters as significant.
◦ There can be no embedded blanks.
◦ Reserved words cannot be used as identifiers.
◦ Identifiers are case sensitive. Therefore, result and Result,
both valid examples of identifiers, are distinct.
 Examples of legal identifiers : student age,
Item_25, counter, area_of_land

 Examples of illegal identifiers :

◦ student age ->embedded blank
◦ continue ->reserved word
◦ 15thFeb ->the first character is a digit
◦ Width Length ->special character +
Tips to choose the name for identifier:
 Program comments : Are explanations or
annotations that are included in a program for
documentation and clarification purposes.
 It describe the purpose of a program, function or
statement. They are completely ignored by the
compiler during compilation, and they have no
effect on program execution.
 A way of documentation within the coding
 To specify comment in C:
◦ /*This is a comments*/ or
◦ // This is another alternative of comment
 Escape sequence indicates “special” character
output
Escape Sequence Name Meaning of Escape Sequence

\a Alert Sounds a beep

\b Backspace Backs up one character
\f Formfeed Starts a new screen or page
\n New line Moves to beginning of next line
\r Carriage return Moves to beginning of current
\t Horizontal tab line
\v Vertical tab Moves to next tab position
\\ Backslash Moves down a fixed amount
\’ Single Prints a backslash
\” quotation Prints a single quotation mark
\? Double Prints a double quotation mark
\000 quotation Prints a quotation mark
Question mark Prints a character whose ASCII
code is a one-to-three-digit
\XHHH octal value
Prints a character whose ASCII
 Punctuations serve as separators for
functions or statements
 Examples:
◦ {} , () , ; , : , …
 Operators can be
◦ Arithmetic operators
 Performing mathematical operation to the operands
(A+B)
◦ Unary operators
 Act on single operand to produce a new value (e.g. -
173)
◦ Relational and logical operators
 For the purpose of comparison (e.g. >, <,>=,!=);
◦ Assignment operators
 Assigning value to identifiers (e.g. +=, ++, --)
◦ Conditioner operators
 Provide conditional statements ((i > 0) ? 0 : 1)
Statements
A statement is a specification of an action to be taken by the
computer as the program executes.

/*Function body*/

printf (“A PROGRAM THAT COMPUTES TOWN INCOME TAX\n”); Output

statement
printf (“Enter gross income: RM ”);
scanf (“%1f”, &gross_income); Input
town_tax = TOWN_TAX_RATE * gross_income; statement

printf (“Town tax is RM %f .”, town_tax); Compute &

stores the
return 0;
result in
the
Each such line is a statement. memory
Each statement causes the processor to do something.

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 There are several types of statements in :
1.Expression statements
2.Selection statements
3.Repetition statements
4.Jump statements
5.Labeled statements
6.Compound statements
 Compound Statement
• Is a list of statements enclosed in braces, { }.
• Can contain any number of statements and
declarations.
• Even though all statements must end with
semicolons, a compound statement does not need
the semicolon delimiter after right brace, }.
Writing
a
Program
#include <stdio.h>

const double TOWN_TAX_RATE = 0.0175;

int main(void)
{
double gross_income;
double town_tax;

printf (“A PROGRAM THAT \COMPUTES TOWN INCOME TAX\n”);

printf (“Enter gross income: RM ”);
scanf (“%1f”, &gross_income);

town_tax = TOWN_TAX_RATE * gross_income;

printf (“Town tax is RM %f .”, town_tax);

return 0;

Take a look and consider the coding above!!!!!

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What is Programming Style?

It is a collection of conventions, rules, and techniques that enable

us to write programs in an elegant yet simple and efficient manner.

Techniques of style are highly personal and subjective and are

mostly a matter of common sense.

In general, it is easier to understand and maintain such a program,

even for someone other than the original developer.

We are going to discuss the following styles:

•Using Comments
•Variable Name
•Naming Style
•Indentation and Code Format
•Clarity
•Whitespace

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Comments
Ideally, a comments serves two purposes:

1. Presents the computer with a set of instructions; and

2. Provides the programmer with a clear, easy-to-read
description of what the programmer does.

A working but uncommented program is a time bomb waiting to

explode.
Sooner or later someone will have to modify or upgrade the
program, and the
/********************************************************
lack of comments will make the job ten times more difficult.
* Program filename: myTesting.c *
* Author: Md Shahid Uz Zaman *
* Purpose: For Class Demonstration *
* Usage: Run the program and message appear *
* Date: 10th September 2012 *
********************************************************/

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•Heading
The first comment should contain the name of the program.
Also include a short description of what it does. You may have
the most amazing program but it is useless if no one knows
what it does.

•Author
You’ve gone to a lot of trouble to create this program. Take
credit for it. Also, if someone else must later modify the
program, he or she can come to you for information and help.

•Purpose
Why did you write this program? What does it do?

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•Usage
In this section give a short explanation of how to run the program.
In an ideal world, every program comes with a set of documents
describing how to use it.
•References
Creative copying is a legitimate form of programming (if you don’t
break the copyright laws in the process). In the real world, it
doesn’t matter how you get a working program, as long as you get
it; but, give credit where credit is due. In this section you should
reference the original author of any work you copied.
•Restrictions
List any limits or restrictions that apply to the program, such as:
The data file must be correctly formatted; the program does not
check for input errors.
•Revision history
This section contains a list indicating who modified the program
and when and what changes have been made.

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Variable Name
A variable is a place in the computer’s memory for storing a value.
Names can be any length and should be chosen so their meaning
is clear.

The following declaration tells C that you are going to use three
integer (int) variables named r, s,Avoid
t: using abbreviations

int r, s, t;
Consider another declaration:
int account_number;
int balance_owed;

However, these examples still lacking of information. (i.e., is the

balance_owed in ringgit or cents?). Therefore, it better if we added
a comment after each declaration explaining what we are doing.
const double TOWN_TAX_RATE = 0.0175 // constant declaration

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Indentation and Code
Format

To make programs easier to understand, most programmers

indent their programs.

The general rule for a C program is to indent one level for each
new block or conditional.

There are two styles of indentation. Use any of the two, but make
sure you are consistent in using the style that you choose.

33
1st Style: braces are put on the same line as the
statements
int main(void) {

/*Variable declarations*/

double gross_income;
double town_tax;

/*Function body*/

printf (“A PROGRAM THAT COMPUTES TOWN INCOME TAX\n”);

printf (“Enter gross income: RM ”);

scanf (“%1f”, &gross_income);

town_tax = TOWN_TAX_RATE * gross_income;

printf (“Town tax is RM %f .”, town_tax);

return 0;

} /*End of function main*/

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2nd Style: puts the curly braces on lines by
themselves
int main(void)
{
/*Variable declarations*/

double gross_income;
double town_tax;

/*Function body*/

printf (“A PROGRAM THAT COMPUTES TOWN INCOME TAX\n”);

printf (“Enter gross income: RM ”);

scanf (“%1f”, &gross_income);

town_tax = TOWN_TAX_RATE * gross_income;

printf (“Town tax is RM %f .”, town_tax);

return 0;

} /*End of function main*/

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 /*Function body*/

printf (“A PROGRAM THAT COMPUTES TOWN INCOME TAX\n”);

printf (“Enter gross income: RM ”);

scanf (“%1f”, &gross_income);

if (gross_income > 10000)

{
printf(“this person is reach!!”);
if (gross_income > 10000)
{
printf(“this person is reach!!”);
}
}
town_tax = TOWN_TAX_RATE * gross_income;

printf (“Town tax is RM %f .”, town_tax);

return 0;

/*End of function main*/

 Clarity
A program should read like a technical paper.

It should be organized into sections and paragraphs. Procedures

form a natural section boundary.

You should organize your code into paragraphs.

It is a good idea to begin a paragraph with a topic sentence

comment and separate it from other paragraphs by a blank line.
// poor programming practice
temp = box_x1;
box_x1 = box_x2;
box_x2 = temp; temp = box_y1;
box_y1 = box_y2;
box_y2 = temp;

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A better version would be:

/* Purpose: Swap the two corners */

/* Swap X coordinate */
temp = box_x1;
box_x1 = box_x2;
box_x2 = temp;

/* Swap Y coordinate */
temp = box_y1;
box_y1 = box_y2;
box_y2 = temp;

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Some styles conventions commonly used to produce
readable code.
1. Insert blank lines between consecutive program sections, as shown
below:
double gross_income;
double town_tax;

printf (“A PROGRAM THAT COMPUTES TOWN INCOME TAX\n”);

printf (“Enter gross income: RM ”);
scanf (“%1f”, &gross_income); town_tax = TOWN_TAX_RATE * gross_income;

2. Make liberal use of clear and helpful comments.

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Example 1:

#include <stdio.h>

int main (void)

{
printf(“Welcome to C!\n”);
return 0;
}
Example 2:

#include <stdio.h>

int main (void)

{

printf(“Welcome”);
printf(“to C!\n|”);

return 0;
}
Example 3:

#include <stdio.h>

int main(void)
{

printf(“Welcome \nto\nC!\n”);
return 0;

}
Any Questions??
1) Print the hello world sentence.

Output:

Hello World!

2) Write simple c program to add two integers.

Output:

Enter first integer

40
Enter second integer
70
Sum is 110
1.Which of the following statements should be used to obtain a
remainder after dividing 3.14 by 2.1 ?

A rem = 3.14 % 2.1;

.
B rem = modf(3.14, 2.1);
.
C rem = fmod(3.14, 2.1);
.
D Remainder cannot be obtain in floating point division.
.
Answer: Option C
Explanation:
fmod(x,y) - Calculates x modulo y, the remainder of x/y.
This function is the same as the modulus operator.
But fmod() performs floating point divisions.
2 Which of the following special symbol allowed in a variable
. name?

A * (asterisk) B | (pipeline)
. .
C - (hyphen) D _ (underscore)
. .

Answer: Option D
Explanation:
Variable names in C are made up of letters (upper and lower case)
and digits. The underscore character ("_") is also permitted. Names
must not begin with a digit.
3 How would you round off a value from 1.66 to 2.0?
.
A ceil(1.66) B floor(1.66)
. .
C roundup(1.66) D roundto(1.66)
. .

Answer: Option A
Explanation: ceil() function truncates a number to its upper
integer.
4 By default a real number is treated as a
.
A float B double
. .
C long double D far double
. .

Answer: Option B
Explanation:
When the accuracy of the floating point number is insufficient, we can
use the doubleto define the number. The double is same as float but
with longer precision and takes double space (8 bytes) than float.
To extend the precision further we can use long double which
occupies 10 bytes of memory space.
 5. Which of the following is a correct comment?
A. */ Comments */
B. ** Comment **
C. /* Comment */
D. { Comment }

Answer: Option C
 6. Which of the following is not a correct variable type?
A. float
B. real
C. int
D. double

Answer: Option B
 7. Which of the following is the correct operator to
compare two variables?
A. :=
B. =
C. equal
D. ==

Answer: Option D
 8. A number such as 45.567 needs to be stored in a variable of
which data type?
A. Int
B. Char
C. Double
D. Real

Answer: Option C
 10. The "\n" character does which of the following operations?
A. Double line spacing
B. Character deletion
C. Character backspace
D. Places cursor on the next line

Answer: Option D