C
is a general-purpose high level language that was originally developed by Dennis Ritchie for the Unix operating system.
It was first implemented on the Digital Equipment Corporation PDP-11 computer
in 1972.
The Unix operating system and virtually all Unix applications are written in the C language. C has now become a widely used professional language for various reasons.
·
Easy
to learn
·
Structured
language
·
It
produces efficient programs.
·
It
can handle low-level activities.
·
It
can be compiled on a variety of computers.
Facts about C
·
C was
invented to write an operating system called UNIX.
·
C is
a successor of B language which was introduced around 1970
·
The
language was formalized in 1988 by the American National Standard Institue
(ANSI).
·
By
1973 UNIX OS almost totally written in C.
·
Today
C is the most widely used System Programming Language.
·
Most
of the state of the art software have been implemented using C
Why to
use C?
C
was initially used for system development work, in particular the programs
that make- up the operating system. C was
adopted as a system development language
because it produces code that runs
nearly as fast as code written in assembly
language. Some examples of the use of C might be:
·
Operating
Systems
·
Language Compilers
·
Assemblers
·
Text Editors
·
Print Spoolers
·
Network Drivers
·
Modern Programs
·
Data Bases
·
Language
Interpreters
·
Utilities
·
C
Program File
All
the C programs are written into text files with extension ".c" for example hello.c. You can use
"vi"(unix) or "notepad"(windows) editor to write your C
program into a file.
You should take certain
steps when you're solving a problem. First, you must define the problem.
If you don't know what the problem is, you can't find a solution! Once you know what the problem
is, you can devise a plan to fix it. Once you
have a plan, you can usually implement it. Once
the plan is implemented, you must test
the results to see whether the problem is solved. This same logic can be applied to many other areas, including
programming.
When
creating a program in C (or for that matter, a computer program in any language), you should follow a
similar sequence of steps:
1.
Determine the
objective(s) of the program.
2.
Determine the
methods you want to use in writing the program.
3.
Create the
program to solve the problem.
4.
Run the
program to see the results.
The
Program Development Cycle
The
Program Development Cycle has its own steps.
1.
In the first step, you use an
editor to create your source code.
2.
In the second step, you compile
the source code to create an object file.
3.
In the third step, you link the
compiled code to create an executable file.
4.
The fourth step is to run the
program to see whether it works as originally planned.
Compiling
the Source Code
Although
you might be able to understand C source code, your computer can't. A computer requires
digital, or binary, instructions in what is called machine language. Before your C program can run on a computer, it must be translated
from source code to machine language.
This translation, the second
step in program development, is
performed by a program called a compiler. The compiler takes your source code file as input
and produces a disk file containing the machine language instructions that correspond to your source
code statements.
Linking
to Create an Executable File
One
more step is required before you can run your program. Part of the C language is a function library that contains object code (code
that has already been compiled) for
predefined functions. A predefined
function contains C code that has
already been written and is supplied in a
ready-to-use form with your compiler package.
Completing
the Development Cycle
Once
your program is compiled and linked to create an executable file, you can run
it by entering its name at the
system prompt or just like you would run any other program. If you run the program and receive results
different from what you thought you would, you need to go back to the first step. You must identify
what caused the problem and correct it in the source code. When you make a change to the source code, you need to recompile and relink
the program to create a corrected version
of the executable file. You keep following this cycle until you get the program
to execute exactly as you intended.
PART B - THE
COMPONENTS OF A C PROGRAM
First
C Program
This
program displays the words Hello, World! on-screen.
#include <stdio.h>
main(){
printf("Hello, World!\n");
}
The
Program's Components
#include
The
#include directive instructs the C compiler to add the contents of an include file into
your program during compilation. An include file is a separate disk file that contains
information needed by your program or the compiler. Several of these files (sometimes
called header files) are
supplied with your compiler. You never need to modify the information in these files;
that's why they're kept separate from your source code.
Include files should all have an .H
extension (for example, STDIO.H).
main()
The
only component that is required in every C program is the main() function. In
its simplest
form, the main() function consists of the name main followed by a pair of empty parentheses
(()) and a pair of braces ({}). Within the braces are statements that make up
the main
body of the program. Under normal circumstances, program execution starts at
the first statement in main() and terminates at the
last statement in main().
printf()
The
printf() statement is a library function that displays information on-screen.
The printf() statement can display a simple text
message or a message and the value of one or more program variables.
Braces
You
use braces ({}) to enclose the program lines that make up every C function-- including
the main() function. A group of one or more statements enclosed within braces is called a block. C has many uses for
blocks.
A
Short C Program
This
is a very simple program. All it does is input two numbers from the keyboard and calculate
their product.
1: /* Program to calculate the product of two numbers. */
2: #include <stdio.h>
3:
4: int a,b,c;
5:
6: main()
7: {
8: /* Input the first number */
9: printf("Enter a number between 1 and 100: ");
10: scanf("%i", &a);
11:
12: /* Input the second number */
13: printf("Enter another number between 1 and 100: ");
14: scanf("%i", &b);
15:
16: /* Calculate and display the product */
17: c = a*b;
18: printf ("%i times %i = %i\n", a, b, c);
19:
20:
21: }
Program
Comments (Lines 1, 8, 12, and 16)
Any
part of your program that starts with /* and ends with */ is called a comment. The compiler
ignores all comments, so they have absolutely no effect on how a program works. You can put anything you want into a comment,
and it won't modify the way
your program operates. A comment can
span part of a line, an entire line,
or multiple lines. Here is an example:
/* A single-line comment */
int a,b,c; /* A partial-line comment */
The
Variable Definition (Line 4)
A
variable is a name assigned to a data storage location. Your program
uses variables to store various kinds of data during
program execution. In C, a variable must
be defined before it can be used. A
variable definition informs the compiler of
the variable's name and the type of data it
is to hold. In the sample program, the
definition on line 4, int a,b,c;, defines three variables--named a, b, and c-- that
will each hold an integer value. A
variable is a name assigned to a data storage location. Your program
uses variables to store various kinds of data during
program execution. In C, a variable must
be defined before it can be used. A
variable definition informs the compiler of
the variable's name and the type of data it
is to hold. In the sample program, the
definition on line 4, int a,b,c;, defines three variables--named a, b, and c-- that
will each hold an integer value.
scanf()
The
scanf() statement (lines 10 and 14) is another library function. It reads data
from the keyboard and assigns
that data to one or more program variables.
PART
C - FUNDAMENTALS OF INPUT AND OUTPUT
The
printf() Format Strings
A printf() format string specifies
how the output is formatted. Here are the three possible components
of a format string:
·
Literal
text is displayed
exactly as entered in the format string.
·
An escape
sequence provides special formatting control. An escape sequence
consists of a backslash (\) followed by a single character. In the preceding
example, \n is an escape sequence. It is called the newline character,
and it means "move to the start of the next line." Escape sequences
are listed in Table 7.1.
·
A conversion
specifier consists of the percent sign (%) followed by a single
character. In the example, the conversion specifier is %i. A conversion
specifier tells printf() how to interpret the variable(s) being printed. The %i
tells printf() to interpret the variable x as a integer.
The most frequently used escape sequences.
Sequence
|
Meaning
|
\n
|
Newline
|
\t
|
Horizontal
tab
|
\\
|
Backslash
|
scanf()
function
This is the function which can be
used to read an input from the command line. Try following program to understand scanf() function.
#include <stdio.h>
main()
{
int x;
int args;
printf("Enter an integer:
");
if (( args = scanf("%d",
&x)) == 0)
{
printf("Error: not an
integer\n");
}
else
{
printf("Read in %d\n", x);
}
}
Here %d is being used to read an
integer value and we are passing &x to
store the vale read input.
Here &indicates the address of variable x.
This program will prompt you to enter a value. Whatever value you
will enter at command prompt that will be output at the screen
using printf() function. If you enter a non-integer value then it will display an error message.
The most commonly needed conversion
specifiers.
Specifier
|
Meaning
|
Types
Converted
|
%c
|
Single
character
|
char
|
%d or %i
|
Signed
decimal integer
|
int, short
|
%ld
|
Signed long
decimal integer
|
long
|
%f
|
Decimal
floating-point number
|
float,
double
|
%s
|
Character
string
|
char arrays
|
%u
|
Unsigned
decimal integer
|
unsigned
int, unsigned short
|
%lu
|
Unsigned
long decimal integer
|
unsigned
long
|
Reserved
Words
The
following names are reserved by the C language. Their meaning is already defined, and they
cannot be re-defined to mean anything else.
PART D - STORING DATA: VARIABLES
Variables
A
variable is a named data storage location in your computer's memory. By
using a variable's name in your
program, you are, in effect, referring to the data stored there.
Variable Names
To
use variables in your C programs, you must know how to create variable names.
In C, variable names must
adhere to the following rules:
·
The
name can contain letters, digits, and the underscore character “_”.
·
The
first character of the name must be a letter. The underscore is also a legal
first character, but it’s not recommended.
·
Case
sensitive. A is different from a.
·
C
keywords can't be used as variable names. A keyword is a word that is part of
the C language.
The following list contains some
examples of legal and illegal C variable names:
Variable Name
|
Legality
|
Percent
|
Legal
|
y2x5__fg7h
|
Legal
|
annual_profit
|
Legal
|
_1990_tax
|
Legal
but not advised
|
Savings#account
|
Illegal:
Contains the illegal character #
|
Double
|
Illegal:
Is a C keyword
|
9winter
|
Illegal:
First character is a digit
|
For many compilers, a C
variable name can be up to 31 characters long. (It can actually be longer
than that, but the compiler looks at only the first 31 characters of the name.)
DO use variable names that are descriptive.
DO adopt and stick with a style for naming your
variables.
DON'T start your variable names with an underscore
unnecessarily.
DON'T name your variables with all capital letters
unnecessarily.
Numeric
Variable Types
C
provides several different types of numeric variables. You need different types
of variables because different
numeric values have varying memory storage requirements
and differ in the ease with which certain
mathematical operations can be
performed on them.
C's numeric data types. Table 1.1
Variable
Type
|
Keyword
|
Bytes
Required
|
Range
|
Character
|
char
|
1
|
-128
to 127
|
Integer
|
int
|
2
|
-32768
to 32767
|
Short
integer
|
short
|
2
|
-32768
to 32767
|
Long
integer
|
long
|
4
|
-2,147,483,648
to 2,147,438,647
|
Unsigned
character
|
unsigned
char
|
1
|
0
to 255
|
Unsigned
integer
|
unsigned
int
|
2
|
0
to 65535
|
Unsigned
short integer
|
unsigned
short
|
2
|
0
to 65535
|
Unsigned
long integer
|
unsigned
long
|
4
|
0
to 4,294,967,295
|
float
|
float
|
32
|
3.4
E-38 to 3.4 E 38
|
Double
precision
|
double
|
64
|
17.4
E-308 to 17.4 E 308
|
Variable
Declarations
Before
you can use a variable in a C program, it must be declared. A variable declaration tells the compiler the name and type of a variable and
optionally initializes the
variable to a specific value. If your
program attempts to use a variable
that hasn't been declared, the compiler generates an error message. A variable
declaration has the following form:
typename varname;
typename specifies the variable type and must be one of the
keywords listed in
Table
1.1. varname is the variable name, which must follow the rules. You can declare multiple
variables of the same type on one line by separating the variable names with commas:
int count, number, start; /* three integer variables */
float percent, total; /* two float variables */
Initializing
Numeric Variables
When
you declare a variable, you instruct the compiler to set aside storage space for the variable. However, the value stored in that space--the
value of the variable--isn't
defined. It might be zero, or
it might be some random "garbage" value.
Before using a variable, you should always
initialize it to a known value. You can
do this independently of the variable declaration by using an assignment statement, as in this
example:
int count; /* Set aside storage space for count */
count = 0; /* Store 0 in count */
PART E - PROGRAM DEVELOPMENT
Set01
(10pts)
Problem:
Create
a C program that will accept 5 numbers and will print out its summation and average.
Sample Output:
Enter 1st Number: 5
Enter
2nd Number: 8
Enter
3rd Number: 5
Enter
4th Number: 4
Enter
5th Number: 6
The
Summation is: 28
The
Average is: 5.6000
Set02
(100pts)
Problem:
Create
a C program that will accept student's grade for prelim, midterm, and final,
then the Final Grade will be
computed by getting 30% of prelim, 30% of midterm and 40% for final.
Sample Output:
Enter
Prelim: 75
Enter
Midterm: 80
Enter
Final: 82
Scoring
Rules:
100
pts If the problem is solved within 30 minutes.
80 pts If the problem is solved within
45 minutes.
70 pts If the problem is solved within
60 minutes.
50 pts If the problem is solved past 61
minutes.
40 pts If the problem is solved past 61
minutes but with runtime errors or bugs.
30 pts for running program with incorrect
output.
0 zero for non running program
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