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Chapter 3

Fundamentals of theC Programming Language

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3.1 INTRODUCTION

This chapter serves as a formal introductionto the C programming language.

The fundamental elements of the Clanguage.

Algorithms requires as least five statementtypes; input, output, arithmetic calculations,

selection, and repetition.

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Analysis

Input. Gross annual income in dollars.Output. The computed city income tax in

dollars.

Formulas. The city income tax is computedusing the formula.

income_tax = 0.0175 * gross_income

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Design

print A PROGRAM THAT COMPUTES

CITY INCOME TAX

print Enter gross income:

read gross_income

compute city_tax = 0.0175 * gross_income

print city_tax

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Implementation

A PROGRAM THAT COMPUTES CITY

INCOME TAX

Enter gross income : 18657City tax is 326.497500 dollars.

The five lines that we have just explained areexamples of C statements. Notice that they

all terminate with a semicolon.

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3.3 LANGUAGE CHARACTER SET AND

TOKENStypes of tokens

1. Reserved words (keywords)

2. Identifiers

3. Constants

4. String literals

5. Punctuators

6. Operators

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1. Reserved words :

Identify language entities, they have special

meanings to the compiler. C reserved words

must be typed fully in lowercase. Someexamples of reserved words from the

program are const, double, int, and return.

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2. Identifiers

programmer-defined words. Needed for programvariables, functions, and other program constructs.

gross_income and city_tax are examples. Must be

unique within the same scope

1. A to Z , a to z , 0 to 9 , and the underscore _

2. The first character must be a letter or an underscore.

3. Only the first 32 characters as significant.

4. There can be no embedded blanks.

5. Reserved words cannot be used as identifiers.

6. Identifiers are case sensitive.

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3. Constants

fixed values CITY_TAX_RATE = 0.0175 is an

example of a constant.Integer Constants

commas are not allowed in integer constants.

Floating-Point Constants

either in conventional or scientific notation. Forexample, 20.35; 0.2035E+2

Character Constants and Escape Sequences

a character enclosed in single quotation marks.

Precede the single quotation mark by a backslash,printf(%c, \);

Escape sequence

causes a new line during printing. \n

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4. String Literals

characters surrounded by double quotation marks.

format specifier for output converts the internalrepresentation of data to readable characters.( %f ) forexample,

City tax is 450.000000 dollars.

precede it with a backslash as

Jim \Mac\ MacDonald

backslash character can be used as a continuationcharacter

printf(THIS PROGRAM COMPUTES \ CITYINCOME TAX);

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5. Punctuators

[ ] ( ) { } , ; : * #

6. Operators

result in some kind of computation or actioncity_tax = CITY_TAX_TATE * gross_income ;

operators act on operands.

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3.4 THE STRUCTURE OF A C PROGRAM

C program consists of followingcomponents:

1. Program comments

2. Preprocessor directives

3. Type declarations

4. Named constants

5. Statements

6. Function declarations (prototypes)7. Function definitions

8. Function calls

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1. Program Comments

use /* and */ to surround comments, or // to begin comment lines.

2. Preprocessor Directives

Lines that begin with a pound sign, #,

A preprocessor directive is can instruction to thepreprocessor. Named file inclusion is concerned with adding the

content of a header file to a source program file. Standard header

files. For example,

#include

#include causes a headerfile to be copied into the code.

programmer-defined header file surrounded by double quotation

marks. #include

to advantage in partitioning large programs into several files.

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3. Data Types and Type Declarations

double gross_income;double city_tax;

variables type determines1. How it is stored internally

2. What operations can be applied to it

3. How such operations are interpreted

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declare a variable to be of type integer, the compilerallocates a memory location for that variable. The

size of this memory location depends on the type ofthe compiler.

int is 2 bytes the range 32768 through 32768designed to perform arithmetic operations and

assignment operations. Two classes of data types:1. Fundamental data types

2. Programmer-defined data types

to classes of built-in data types:

1. Fundamental data types

2. Derived data types

Examples of derived data types are arrays, strings,and structures.

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Data Type int

Data Type char

Data Type double

Data initialization

be initialized in two ways,

1. Compile-time initialization

2. Run-time initialization

Strings as a Derived Data Type

A string is a sequence of characters that istreated as a single data item. A string variable is a

variable that stores a string constant.

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how to declare string variables.

1. Begin the declaration with the keyword

char, Char report_header [41]

2. To initialize a string variable at complietime,

char report_header [41] = Annual Report

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4. Named Constants

const double CITY_TAX_RATE = 0.0175;is an identifier whose value is fixed and does not

change during the execution of a program in

which it appears.

In C the declaration of a named constant begins

with the keyword const.

During execution, the processor replaces every

occurrence of the named constant .

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5. Statements

A statement is a specification of an action tobe taken by the computer as the program

executes.

Compound Statements

is a list of statements enclosed in braces, { }

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3.5 A FIRST LOOK AT FUNCTIONS

as a block of code that performs a specific task.

The function main( )

int main(void) {

Statement;

Statement;

return 0;

}

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return statement ensures that the constant value

0, the program status code, is returned to theprogram or the operating system that has

triggered the execution of this function main.

Each C program must have one main function.

The type specifier for functions can be int,double, char, void, and so on, depending on

the type of data that it returns.

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3.6 BUILDING A MINIMUM LANGUAGE SUBSET

An expression is a syntactically correct andmeaningful combination of operators and operands.

city_tax = CITY_TAX_RATE * gross_income

An expression statement is any expression followed by

a semicolon.

city_tax = CITY_TAX_RATE * gross_income

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Example 3.2

area ? short_side 10.05 long_side 20.00

area = short_side * long_side

area 210.00 short_side 10.05 long_side 20.00

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The Standard Output Function printf

This statement is a function call to the standard

library function printf. The parentheses ( ) are

known as the function call operator.

Following compilation, the linker fetches the

object code corresponding to printf from thestandard C library and combines it with your

object program.

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Quantity Type printf Format Specifier

int %d

double %f or % lf char %c

printf(Your year of birth is %d, and in2000 you will be %d years old. ,year_of_birth, 2000 year_of_birth);

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Variable Type scanf Format Specifier

int %d

double %lf

char %c

printf(Type your weight in pounds: );

scanf(%d , &weight_in_pounds);

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Input of String Variables

char string1 [31];scanf(%s , string1);

The reason is that scanf skips whitespaceduring string input and picks string valuesdelimited by whitespace.

the input string values that contain

whitespace, we can use several techniquesin C. We will explain one easy way, whichrequires the use of the gets function.

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3.7 PREPARING C SOURCE PROGRAM

FILESHere are some style conventions

1. Insert blank lines between consecutive

program sections.2. Make liberal use of clear and help comments.

3. Keep your comments separate from the

program statements.4. Type each statement or declaration on a

single line.

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5. Avoid running a statement over multiple

lines.6. Avoid line splicing.

7. Indent all lines that form a compound

statement by the same amount.8. Type the beginning and end braces, { },

for compound statements

9. Use whitespace in typing statements.10. Conclude each function by a comment

to mark its end.

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3.8 EXAMPLE PROGRAM 2 : A C Programthat Converts Height and Weight to MetricUnits

Enter your first name : Kelly

Enter your last name : Johnson

Enter your height in inches : 64

Enter your weight in pounds : 110

Kelly Johnson, your height is 162.560000centimeters, and your weight is 49.894900kilograms.

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3.9 PROGRAM DEBUGGING

1 #include

2

3 int main (void) {

4 double number;5

6 printf(Enter a number : )

7 scanf(%lf , &number);

8 Inverse = 1.0 / number ;

9 printf(Inverse of %f is %f , number, inverse);

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---Configuration : debug Win32 Debug ---

Compiling

Debug.cD:\cprogs\debug.c(7) : error C2146: cyntax error :

missing ; before identifier scanf

D:\cprogs\debug.c(8) : error C2065 inverse :

undeclared identifier.D:\cprogs\debug.c(8) : warning C4244 : = :

conversion from const double to int , possibleloss of data.

D:\cprogs\debug.c(10) : fatal error C1004 :unexpected end of file found

Error executing c1.exe

Debug.exe 3 error(s), 1 warning(s)

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Debugging for Warning Diagnostics

do not force it to stop the compilation.

Debugging Run-Time Errors

Enter a number : 0

Floating point error : Divide by 0 .

Abnormal program termination .

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if number is equal to zero

print Zero does not have a finite inverse.

else

compute inverse = 1 / number

end_if