Program
A computer program (also software, or just a program) is a
sequence of instructions written in a sequence to perform a
specified task with a computer.
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Programming
Fundamentals I
BSCS Semester1
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Diagrammatic Representation of Program Execution Process
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Execution of C Program
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Preprocessing
Using a Preprocessor program to convert C source code in expanded source code. "#includes"
and "#defines" statements will be processed and replaced actually source codes in this step.
Compilation
Using a Compiler program to convert C expanded source to assembly source code.
Assembly
Using a Assembler program to convert assembly source code to object code.
Linking
Using a Linker program to convert object code to executable code. Multiple units of object codes
are linked to together in this step.
Loading
Using a Loader program to load the executable code into CPU for execution.
http://www.ustudy.in/node/10273
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Structure of C Program
To include header
files in our
program
Contains built-in-functions. These are also
called pre-defined or already developed
functions
Header File
Preprocessor
Directives
Angle or pointed
brackets
h stands for header file
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Return type of
main function. It is
used to determines
whether the
program is
executed
successfully or not.
Void means
Body
nothingBegin
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#include<stdio.h>
#include<conio.h>
void main( )
{
Function
Name
main
function
Starting point of
program execution
Parenthesis shows function. It is used to pass
parameters/arguments
printf(“Welcome to Computer Scientists”);
getch();
Program
Body
Body End
File name(standard input
output )
}
printf stands for print function. It will print the output
on the monitor
Get character
function. It get a
character at
runtime. But we use
it to stay screen to
see output
String or message to be
displayed on monitor. It must be
enclosed in double quotes(“ “)
Each statement must
end with semicolon. A
statement without
semicolon generates
syntax error.
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Simple Steps to write and run a program in C.
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3.
Go to this path C:\TC\BIN then double click on
short to open C language.
Now save your program by choosing a
meaningful program file name. e.g. welcome.c is
a file name for a program that will display
welcome message at runtime.
Now write your program as explained in the
previous slide. (translation of algorithm to a c
program).
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4. Press Alt+F9 key to compile program. If your program is error
free then following screen will appear:
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5. Now press Ctrl+F9 key to run the program. Following screen
shows the output of the program:
Now press enter to go back to the source code of the program
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Now see the following sample program.
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Formatted Input Statement
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scanf()
The scanf function allows you to accept input from standard in, which for us is generally the
keyboard.
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Syntax:
scanf(”control string”, &variable01, &variable02, …);
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Example:
scanf(”%d”, &number);
E.g. Program
#include <stdio.h>
int main()
{ int a, b, c;
printf("Enter the first value:");
scanf("%d", &a);
printf("Enter the second value:");
scanf("%d", &b);
c = a + b;
printf("%d + %d = %d\n", a, b, c);
return 0;
}
http://computer.howstuffworks.com/c6.htm
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Formatted Output Statement
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Printf() : ( Output function )
It displays information on screen.
It returns the number of characters printed.
It displays the text you put inside the double quotes.
It requires the backslash character(escape sequence) to display some special characters.
It can display variables by using the % conversion character.
Printf format: a string argument followed by any additional arguments.
Syntax :
printf("control string",list);
where control string gives the format of data to be displayed, list contains the list of
variables, constants, array names to be printed. The general form is
%w.p data type
where % - conversion specification indicator
w - width of output data(optional)
p - Number of digits after decimal point or number of characters to to
displayed from a string
data type - type of output data or conversion character
Printing Integer Numbers :
The general format of control string to output an integer is
%wd
where w - width of output data(optional)
d - conversion character for integer
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Rules :
If there is no width then the output number will be printed as such.
If the output number width is greater than the width specified then it will be printed in full
irrespective of the width.
The number printed is right justified. This can be changed by left by placing a minus sign after %
character.
If the width specified is greater than the width of the output number, then the unused position is
left blank.
The unused leading blanks in the output can be made to zero by placing a zero before the width
w.
To print numbers with + or - sign, the sign should be placed before the variable.
Example :
Assume x=2000;
Format
Output
printf("%d",x);
2000 // Rule 1
printf("%3d",x);
2000 // Rule 2
printf("%5d",x)
2000 // Rule 4
printf("%-5d",x);
2000
// Rule 3
printf("%07d",x);
0002000 // Rule 5
printf("%4d",-x);
-2000 // Rule 6
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Printing Real Numbers :
The general format of control string to output a real number is
%w.p f or e
where w - width of output data(optional)
p - number of digits after decimal point
f - conversion character for floating point without exponent
e - conversion character for floating point with exponent
Rules :
If no decimal place count(p) is placed, the default is 6 places.
If a number contains more than 6 decimal places, the result will be rounded to 6 places.
The integer part of a number is right justified and the decimal part is left justified.
By placing a - sign after % character the integer part can be made to left justified.
To print a number with + or - sign the sign should be placed before the variable.
Example :
Assume x=123.4678;
Format
Output
printf("%8.4f",x);
123.4678
printf("%f",x);
123.467800
printf("%e",x);
1.234678e+02
printf("%-8.2f",x);
123.47 (left justified)
Printing strings :
The general format of control string to output a string is
%w.ps
where w - width of the string(optional)
p - number of characters to be printed from the beginning
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Rules :
If the width of the string is greater than the width specified, the string will be printed in full.
The output is right justified.
By placing a - sign after % character it can be changed to left justified.
Example :
Assume college="mspvl";
Format
Output
printf("%s",college);
mspvl
printf("%10s",college);
mspvl
printf("%3s",college);
mspvl
printf("%5.2s",college);
ms
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Another Sample Program
Program:
#include<stdio h>
void main()
{
int number;
printf(”Enter an integer: \n”); //prompt message
scanf(”%d”, &number);
//read message
printf(”The number you entered is: %d”, number);
getch();
}
Output:
Enter an integer:
25
The number you entered is: 25
Rules:
• The ampersand symbol, &, is very important.
•It’s an operator specifying the variable name’s address.
•Omitting it, might result into unexpected results.
•We dont use ampersand(&) symbol in front of the string_name.
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Comments
Non - executable statements
Comments are used for program
documentation
Two formats
Single Line Comments
// This program is used to show the Welcome
Message.
Multi Lines Comments
/*
This program is used to show the
square of even numbers from 10 to
100.
*/
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Tokens
Tokens are individual words and punctuation marks in passage of text.
In C, program the smallest individual units are known as C Tokens. C
has Six types of Tokens. The Tokens are shown in figure. C programs
are written using these tokens and the syntax of the language.
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General form of a C++ program
// Program description
#include directives
int main()
{
constant declarations
variable declarations
executable statements
return 0;
}
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C++ compiler directives
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The #include directive tells the compiler to include
some already existing C++ code in your program.
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The included file is then linked with the program.
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There are two forms of #include statements:
#include <iostream> //for pre-defined
#include "my_lib.h"
files
//for user-defined files
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C++ keywords
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Each keyword has a predefined purpose in
the language.
Do not use keywords as variable and
constant names!!
Exmples: bool, break, case, char, const,
continue, do, default, double, else, extern,
false, float, for, if, int, long, namespace,
return, short, static, struct, switch,
typedef, true, unsigned, void, while
etc
etc..
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C++ identifiers
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Variable: Location in memory where value can be stored
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An identifier is a name for a variable, constant, function, etc.
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Series of characters (letters, digits, underscores)
Cannot begin with digit
Are Case sensitive
Cannot have special characters in them.
Examples of valid identifiers:
First_name, age,
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y2000,
y2k
Examples of invalid identifiers:
2000y, X=Y, J-20, ~Ricky,*Michael
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Identifiers are case-sensitive. For example: Hello, hello,
WHOAMI, WhoAmI, whoami are unique identifiers.
http://www.ustudy.in/node/2897
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Programming Style
C++ is a free-format language, which means that:
 Extra blanks (spaces) or tabs before or after identifiers/operators are
ignored.
 Blank lines are ignored by the compiler just like comments.
 Code can be indented in any way.
 There can be more than one statement on a single line.
 A single statement can continue over several lines.
In order to improve the readability of your program, use the following
conventions:
 Start the program with a header that tells what the program does.
 Use meaningful variable names.
 Document each variable declaration with a comment telling what the
variable is used for.
 Place each executable statement on a single line.
 A segment of code is a sequence of executable statements that belong
together.
 Use blank lines to separate different segments of code.
 Document each segment of code with a comment telling what the 25
segment does.
Variables
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As a programmer, you will frequently want your program to "remember" a value. For
example, if your program requests a value from the user, or if it calculates a value,
you will want to remember it somewhere so you can use it later. The way your
program remembers things is by using variables. For example:
int b; This line says, "I want to create a space called b that is able to hold one integer
value." A variable has a name (in this case, b) and a type (in this case, int, an
integer). You can store a value in b by saying something like:
b = 5; You can use the value in b by saying something like:
printf("%d", b); In C, there are several standard types for variables:
int - integer (whole number) values
float - floating point values
char - single character values (such as "m" or "Z")
We will see examples of these other types as we go along.
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Rules to Declare an
Identifier (variable)
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Alphabets from A to Z or a to z
The digits from 0 to 9
Underscore(_) can be used
The first character of an identifier can not be a digit
The name of an identifier can not be a reserve word
No space allowed in the name of identifier
Valid Name:
A
Student_Name
_Fname
Pi
Inalid Name:
$Sum //special ch.
6StName // 1st letter digit
F name // no space allowed
int // reserve word
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Identifier (variable)
Declaration
Syntax
Data-Type Space Variable-Name(Indentifier);
e.g.
int frstNumber;
char choice;
float divide;
long output;
Identifier (variable)
Initialization
Syntax
Data-Type Space Variable-Name(Indentifier) = Value;
e.g.
int frstNumber=10;
char choice=‘y’;
float divide=0.0;
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How many bytes I am eating?
integer
data
short
2 bytes
int
2 bytes(16 bit system)
4 bytes (32 bit system)
long
4 bytes
float
4 bytes
double
8 bytes
long double
10 bytes
Character
char
1 byte
Boolean
bool
1 byte
Floating
point data
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Assignment Operator (=)
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= (assignment operator)
 Assigns value to variable
 Binary operator (two operands)
 Example:
sum = variable1 + variable2;
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Memory Concepts
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Variable names
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Correspond to actual locations in computer's
memory
Every variable has name, type, size and value
When new value placed into variable, overwrites
previous value
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Memory Concepts
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cin >> first;
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first
45
first
45
second
72
first
45
second
72
cin >> second;
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Assume user entered 45
Variable
Identifier
Assume user entered 72
sum = first + second;
sum
117
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Arithmetic
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Rules of operator precedence
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Operators in parentheses evaluated first
 Nested/embedded parentheses
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Operators in innermost pair first
Multiplication, division, modulus applied next
 Operators applied from left to right
Addition, subtraction applied last
 Operators applied from left to right
Operator(s)
Operation(s)
()
Parentheses
*, /, or %
+ or -
Order of evaluation (precedence)
Evaluated first. If the parentheses are nested, the
expression in the innermost pair is evaluated first. If
there are several pairs of parentheses “on the same level”
(i.e., not nested), they are evaluated left to right.
Multiplication Division Evaluated second. If there are several, they re
Modulus
evaluated left to right.
Addition
Evaluated last. If there are several, they are
Subtraction
evaluated left to right.
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Thank
You
New
Computer
Scientists
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