Chapter 3
Fundamentals of the
C Programming Language
1
3.1 INTRODUCTION
This chapter serves as a formal introduction
to the C programming language.
The fundamental elements of the C
language.
Algorithms requires as least five statement
types; input, output, arithmetic calculations,
selection, and repetition.
2
3.2 EXAMPLE PROGRAM 1: A C Program that
Computes City Tax
Requirements Specification Develop a program
that does the following
1. Prints on the monitor screen a brief description
of the program’s purpose.
2. Prompts the user to enter a value for gross
annual income using the terminal keyboard.
3. Reads a value for gross income.
4. Computes the city income tax for the city of
Oxford, Ohio. The city income tax is 1.75
percent of the gross annual income.
5. Prints the computed city income tax.
3
Analysis
Input. Gross annual income in dollars.
Output. The computed city income tax in
dollars.
Formulas. The city income tax is computed
using the formula.
income_tax = 0.0175 * gross_income
4
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
5
Implementation
A PROGRAM THAT COMPUTES CITY
INCOME TAX
Enter gross income : 18657
City tax is 326.497500 dollars.
The five lines that we have just explained are
examples of C statements. Notice that they
all terminate with a semicolon.
6
3.3 LANGUAGE CHARACTER SET AND
TOKENS
types of tokens
1. Reserved words (keywords)
2. Identifiers
3. Constants
4. String literals
5. Punctuators
6. Operators
7
1. Reserved words :
Identify language entities, they have special
meanings to the compiler. C reserved words
must be typed fully in lowercase. Some
examples of reserved words from the
program are const, double, int, and return.
8
2. Identifiers
programmer-defined words. Needed for program
variables, 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.
9
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.
For
example, 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
10
4. String Literals
characters surrounded by double quotation marks.
format specifier for output converts the internal
representation of data to readable characters.( %f ) for
example,
City tax is 450.000000 dollars.
precede it with a backslash as
“Jim \”Mac\” MacDonald”
backslash character can be used as a continuation
character
printf(THIS PROGRAM COMPUTES \ CITY
INCOME TAX”);
11
5. Punctuators
[ ] ( ) { } , ; : ………* #
6. Operators
result in some kind of computation or action
city_tax = CITY_TAX_TATE * gross_income ;
operators act on operands.
12
3.4 THE STRUCTURE OF A C PROGRAM
C program consists of following
components:
1. Program comments
2. Preprocessor directives
3. Type declarations
4. Named constants
5. Statements
6. Function declarations (prototypes)
7. Function definitions
8. Function calls
13
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 the
preprocessor. Named file inclusion is concerned with adding the
content of a header file to a source program file. Standard header
files. For example,
#include <stdio.h>
#include causes a headerfile to be copied into the code.
programmer-defined header file surrounded by double quotation
marks. #include <d:header1.h>
to advantage in partitioning large programs into several files.
14
3. Data Types and Type Declarations
double gross_income;
double city_tax;
variable’s type determines
1. How it is stored internally
2. What operations can be applied to it
3. How such operations are interpreted
15
declare a variable to be of type integer, the compiler
allocates a memory location for that variable. The
size of this memory location depends on the type of
the compiler.
int is 2 bytes the range –32768 through 32768
designed 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.
16
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 is
treated as a single data item. A string variable is a
variable that stores a string constant.
17
how to declare string variables.
1. Begin the declaration with the keyword
char, Char report_header [41]
2. To initialize a string variable at complie
time,
char report_header [41] = “Annual Report”
18
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 .
19
5. Statements
A statement is a specification of an action to
be taken by the computer as the program
executes.
Compound Statements
is a list of statements enclosed in braces, { }
20
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;
}
21
return statement ensures that the constant value
0, the program status code, is returned to the
program 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.
22
3.6 BUILDING A MINIMUM LANGUAGE SUBSET
An expression is a syntactically correct and
meaningful 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
23
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
24
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 the
standard C library and combines it with your
object program.
25
Quantity Type
printf Format Specifier
int
double
char
%d
%f or % lf
%c
printf(“Your year of birth is %d, and in
2000 you will be %d years old.” ,
year_of_birth, 2000 – year_of_birth);
26
Variable Type
int
double
char
scanf Format Specifier
%d
%lf
%c
printf(“Type your weight in pounds: “);
scanf(“%d” , &weight_in_pounds);
27
Input of String Variables
char string1 [31];
scanf(“%s” , string1);
The reason is that scanf skips whitespace
during string input and picks string values
delimited by whitespace.
the input string values that contain
whitespace, we can use several techniques
in C. We will explain one easy way, which
requires the use of the gets function.
28
3.7 PREPARING C SOURCE PROGRAM
FILES
Here 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.
29
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.
30
3.8 EXAMPLE PROGRAM 2 : A C Program
that Converts Height and Weight to Metric
Units
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 162.560000
centimeters, and your weight is 49.894900
kilograms.
31
3.9 PROGRAM DEBUGGING
1 #include <stdio.h>
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);
32
---Configuration : debug – Win32 Debug --Compiling …
Debug.c
D:\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 ‘ , possible
loss 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)
33
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 .
34
if number is equal to zero
print “Zero does not have a finite inverse.”
else
compute inverse = 1 / number
end_if
35