05 Program Structure and Construction

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Introduction to C Programming

Lexical Elements ,Data types and

the C system


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CT018-3-1 Introduction To C Programming Program Structure and Construction

Topic & Structure of the lesson

In this chapter you will learn about:

C program structureStandard library and function

Types of errors


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Learning Outcomes

If you have mastered this topic, you should be ableto use the following terms correctly in your

assignments:

Preprocessor directive

Stdio.h

Main function

Comments

Constants Expression

Syntax, logical and runtime errors


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Constants

Constantsareentities that appear in theprogram code as f ixed values.

For Example:-

const double taxrate=0.0175; Character Constant: Is acharacter enclosed in sing le quo tat ionmarks.

Some examples of character constants are 1,aand A.


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Constants

Example 1:-

The output statement,

printf(%c,T);

will print the letter Ton the screen.

Example 2:-

char S=a;

printf(%c,S);

will print the letter S on the screen.


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String Constants

String Constant:

A string literal or string constant is a

sequence of any number of characters

surrounded by double quo tat ionmarks. Following are examples of String Constants.

This is a String Constant

125

Is this Johns car?


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Statements

A statementis a Speci f ication of an act ionto be taken by the computer as the program

executes.

Each C statement must end with thepunctuator/ separator semicolon (;).

For Example:-

c= a+b; But, some of the statements should not end

with semicolon.

For Example, while ( I



Expressions

An Expressionis a combination of bothOperatorsand Operands.

For Example:-

city_tax = taxrate * gross_income;

c= a + b;

area = 2 * pi * r;



Standard Output function printf()

The Syntax for the print f()function is,

printf(Format Control String);

printf(Format Control String, print list);

For Example :-

printf(Enter your age:);

printf(%d, age);

printf(Your age of birth is %d, yob );



Standard Input function scanf()

The Syntax for the scanf()function is,

scanf (Format Control String, print list);

Example 1:-

printf(Enter your age:);

scanf(%d,&age);

printf(Type your weight in inches:);

scanf(%d,&weight);


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Structure of a C Program

C program consists of the followingcomponents:

Program Comments

Preprocessor directives

Type declarations

Named Constants

Statements

Function definitionsFunction Calls



Example for a C Program

/* Program to find area of a circle*/

#include

main()

{int radius;

double area;

const double pi=3.14;

printf(\nEnter the radius value:);

scanf(%d,&radius);

area=2*pi*radius;Statements

Program

commentsPreprocessor

Directives

Type

DeclarationsNamed

Constants



Example for a C Program

printf(\n Area of a Circle =

%d,area);

}

OUTPUT:

Enter the radius value: 2

Area of a Circle = 12.56



Program Comments

Commentsare explanat ionsor annotat ionsthat are included in a program for

documentationand clarification purposes.

They are completely ignoredby thecompiler dur ing compi lat ion,and they

have no effect on program execution.

There are two types of comments:

Multiple line comment is represented

by /**/



Program Comments

Single line comment is represented by // For Example :-

1. /* This Program is used to calculate

the Factorial of a number */2. // Program to add two numbers

3. // Program to find area of a Circle

Comments are meant to aid,never to hamper, readability.



Preprocessor Directives

preprocessor modifies the text of a Cprogram before compilation.

A preprocessor directive starts with #

#includeinstructs the preprocessorto include the contents of the standardinput .output(stdio.h), in the program, inorder to use certain functions printf andscanf.

Constant double pi=3.14 associates theconstant macro pi with the meaning 3.14.


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main()Function

Every C program has a mainfunction, whereprogram execution begins.

A function definition consists of headerand a

body. header:consists of the name of the function

and the parameter list enclosed within the

parenthesis().

body: consists of declarat ionsand executablestatements both enclosed in braces {},known

as block.


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main()Function

main ()

{

float inches,cm;

/* variable declaration */

printf(Enter a length in inches:

);

/* ... rest of statements follow ...*/

}


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Types of Errors

Errorsare classified into three types:

Syntax Errors

Logical Errors

Runtime Errors


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Logical Errors

Logic errorsgo unnoticed by the

compiler, but they cause fatal

errors in the outcome of aprogram. Exampleis not

producing the required or

expected output.


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Runtime Errors

Runtime errorsattempt to

perform some illegal operations

when it executes. Exampleisdividing by zero.


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A Sample Program

Problem: Conversion from inches to centimeters

Recall the first step in problem solving:

Understand the problem

What is the Input?

Length in inches.Lets call it inches.

What is the Output?

Length in centimeters.Lets call it cm.


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A Sample Program

Step 2: Devise a p lan

What is the relationship between the input and

the output?

one inch = 2.54 centimeters

So the algorithm is:

get the length in inches

compute length in centimeters

report length in centimeters


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A Sample Program

Step 3:Carry out the plan

Do I know how to compute the length in

centimeters?

Yes.compute length in centimeters

length in centimeters is 2.54 *length in inches

Is the plan(algorithm) correct?Work out on some examples.

Now move from algorithm to writing program.


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A Sample Program

/* Program to convert from inches into centimeters*/#include

#define CM_PER_INCH 2.54

main()

{

float inches, cm;

printf(Enter the length in inches:);

scanf(%f,&inches);cm= CM_PER_INCH * inches;

printf(That equals %.2f centimeters\n,cm);}


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Output

Enter the length in inches: 2

That equals 5.08 centimeters

05 Program Structure and Construction

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