Computer Fundamentals-2

Instructor
Mr. S.Christalin Nelson
01-Sep-2017
Computer Fundamentals - II

At a Glance
• Generation of Programming Languages
• Programming Paradigms
• Structure & Execution Environment of a Basic C Program
• Need of Translators, Linkers, Locaters, Loaders & Editors
• Software Engineering & Problem Solving Methods
• Few Inclusions from C99 and C11 Standards
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Generations
• Generation -1: Machine Level Programming Languages (late
1940s)
• Generation -2: Assembly Languages (early 1950s)
• Generation -3: High-Level Languages (mid 1950s to present)
• Generation -4: Specification/Query Language, Report
Generators (1970s to present)
• Generation -5: Artificial Intelligence
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Features of Languages (1/2)
• Machine Level Language
– Fast and efficient, executed directly on the CPU
– Consists only of 0s and 1s
– Difficult for humans to read, write, and debug
• Assembly Language
– Also included Interpreting Routines & early Compilers
– Simple mnemonic instructions <opcode> <operands>
– Assembler translates into machine code
– Hand coding in assembly only for low-level needs
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Features of Languages (2/2)
• High Level Languages
– Easier for humans to read, write, debug
– Compiler translates into machine code before running
– Interpreter translates into machine code at runtime
– Examples: FORTRAN, LISP, COBOL, ALGOL (Ada, Basic, C, C++,
Java, Pascal, Smalltalk, …)
• Fourth Generation
– Examples: Maple, Mathematica, Postscript, SPSS, SQL
• Fifth Generation
– Examples: Prolog
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Family Tree of Languages
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Fortran
BASIC
Cobol
LISP
Scheme
ML
Prolog
PL/1
Algol 60
Algol 68
Pascal
Modula 3
Ada
C
C++
Simula
Smalltalk
Java
Dylan
Ruby
Perl
PythonC#
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Procedural Paradigm
• Procedures, sequential execution of code are basic building
blocks of program.
• Examples
– FORTRAN (FORmula TRANslating; John Backus, IBM, 1950s)
– ALGOL (ALGOrithmic Language, 1958)
– COBOL (COmmon Business Oriented Language, 1960)
– BASIC (Beginner's All-purpose Symbolic Instruction Code, John
Kemeny and Thomas Kurtz, Dartmouth, 1963)
– Pascal (Niklaus Wirth, 1970)
– C (Dennis Ritchie, Bell Labs, 1972)
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Object Oriented Paradigm
• Program is designed around the objects and classes required
to solve the problem.
• Examples
– Smalltalk (Alan Kay, Xerox PARC, 1971)
– Ada (US Dept of Defense, 1975)
– C++ (Bjarne Stroustrup, Bell Labs, 1983)
– Java (James Gosling, Sun Microsystems, 1995)
– C# (Microsoft, 2000)
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Alan Kay
B. Stroustrup J. Gosling
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Functional Paradigm
• Program is designed around the evaluation of functions,
rather than modifying state
• Examples
– LISP (John McCarthy, MIT, 1958)
– Common Lisp
– Dylan
– Logo
– Scheme
– ML (Robin Milner et al, Edinburgh, 1970s)
– Haskell (purely functional language, 1990)
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Logic & Scripting Paradigms
• Logic
– Program is declarative, based on mathematical logic
– Example: Prolog (1972)
• Scripting
– Used for text processing, shells, HTML, CGI
– Examples
• awk (Aho, Weinberger, Kerningham, Bell labs, 1978)
• Perl (Larry Wall, NASA, 1987)
• Tcl/Tk (John Ousterhout, 1988)
• Python (Guido van Rossum, CWI, 1991)
• PHP (Rasmus Lerdorf, 1995)
• Ruby (Yukihiro Matsumoto, 1996)
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History of C Language
• Kenneth Thompson and Dennis Ritchie at Bell Labs in 1972
• History
– International Group, ALGOL (1960)
– Martin Richards, BCPL (1967)
– Ken Thompson, B (1970)
– Dennis Ritchie, Traditional C (1972)
– Kernighan & Ritchie, K&R C (1978)
– Standardization (incompatible code of different compilers)
• In 1983, ANSI (American National Standard Institute) started
defining a standard for C called ANSI-C. ANSI-C was adopted by
ISO in 1990 renamed to C89 (Officially ANSI/ISO 9989:1990)
• C99 (Officially ISO/IEC 9899:1999)
• C11 (Officially ISO/IEC 9899:2011)
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Brian Kernighan and D. Ritchie
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C Language
• High Level Procedural Language
• Features
– Coded routines of UNIX OS
– Concise syntax
– Programs a Efficient and Fast
– Highly portable
– Case-sensitive
– No built-in operations for handling composite data types such
as strings, sets, and lists
• Suited for writing both System software and Business
packages (E.g. C Compilers)
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Basic Structure of C Program
Documentation Section (Comments)
Link Section (Link functions from System Library)
Definition Section (Define Symbolic Constants)
Global Declaration Section (Global Variables & User Defined Fn.)
main() Function Section
{
Declaration Part
Executable Part
}
Subprogram Section
User-Defined Functions
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Sample C Program
• Problem: Sum of two Numbers
//my first program to explain the structure
#include <stdio.h> //preprocessor directive
void main() //Program Entry: main() fn.
{ //Start of Program
int a, b, sum; //declaration of variables
printf(“Enter value of a & b: ”); //Output: printf() built-in fn.
scanf(“%d %d”, &a, &b); //Input: scanf() built-in fn.
sum = a + b; //Arithmetic expression/stmt.
printf(“Sum: %d”, sum);
} //End of Program
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Preprocessor Directives
• Provides instruction to the compiler before the actual program
execution begins
• Hash symbol (#)
• Types (partial list)
– # include <headerfile.h>
• Specify header file which holds prototype definition of built-in
functions. Compiler informs linker to link these files with program
• Example: #include <stdio.h>
– “stdio.h” contains prototype definition of printf() and scanf()
– # define const_name const_value
• Defines Symbolic constants
• Example: # define PI 3.14
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Function Definition
• Definition: Function/Procedure/Sub-routine
– Set of Instructions that are executed to achieve a particular
task
– Code reusability
• Types
– Built-in Functions (System Defined)
• E.g. printf(), scanf()
– User-defined Functions
• Syntax
return_type function_name(Argument list)
{ //fn. Definition starts
Set of Instructions //fn. body
} //fn. Definition ends
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Program Input
• scanf() function
– Input from Standard Input
– Prototype definition available in stdio.h
• E.g. scanf(“%d %d”, &a, &b);
– Format String
• Specifies the expected data type format of the input variables
using corresponding format specifiers
– Address-of Operator (&)
• Provides the memory address of the input variable were the
input value is to be stored
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Program Output
• printf() function
– Output to Standard Output
– Prototype definition available in stdio.h
– Format
• Print a String
– E.g. printf(“Hello”); //Output String “Hello”
• Print a value within a String
– E.g. printf(“Sum: %d”, sum); //Value of sum is printed with String
– Format specifier (E.g. %d)
» Specifies the expected data type format of the output variable
whose value is to be printed within the Output String
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Format Specifiers in C (1/2)
Format Specifier printf() scanf()
%c Prints a single character Read a character
%d Prints a signed decimal integer Read a signed decimal integer
%i
Prints a signed decimal
integer
Read a signed integer depending
upon the prefix
- a hexadecimal integer if prefix
is 0x
- a signed octal if prefix is 0
- if no prefix read signed decimal
integer
%u
Prints an unsigned decimal
integer
Unsigned decimal integer
%o Prints an unsigned octal integer Unsigned octal integer
%x
Prints an unsigned hexadecimal
using a,b,c,d,e,f
Read unsigned hexadecimal integer
%X
Prints an unsigned hexadecimal
using A,B,C,D,E,F
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Format Specifiers in C (2/2)
Format Specifier printf() scanf()
%f
A floating point with 6 digits after
decimal point
Read floating point number
%e
Floating point in exponential
format with e
Read floating point number
%E
Floating point in exponential
format with E
%g
Float in %f or %e whichever is
shorter
Floating point number
%G
Float in %f or %E whichever is
shorter
%s String Read a string (till null character)
%% Prints % sign Not applicable
%p
Prints address in hexadecimal
format
Not applicable
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Program Execution (1/7)
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Preprocessing
Program Compilation
Linking
Locating
• Steps involved
Loading
Program Execution
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Program Creation
Source Code (*.c)
Expanded Source Code (*.i)
Object Code
Executable Object Code
Assembly Code
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• Preprocessor Stage
– The following occurs to the Source code
• Header Files are expanded
• Comments are removed
• Macros are replaced
– To print the expanded code on terminal after preprocessing,
the command in Linux is
• $cc -E file_name.c
– To obtain the expanded code in a file the command in Linux is
• $cc -E file_name.c -o file_name.i
– After above said command is executed, a file “file_name.i” is
generated in present working directory and whole code obtained
after pre-processing stage is stored in this file. This file can be
opened for viewing the whole content.
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• Compilation Stage
– Considered to include (1) Compiler Stage & (2) Assembler Stage
• Compiler Stage
– At compilation stage an assembly code (with .s as extension) is
generated on the basis of Source code i.e. depending upon the
functions and structures used in the C program.
– To obtain the assembly code the foll. commands can be used
• $cc –S file_name.c OR $cc –S file_name.i
• Note: Assembler accept files with .i or .c extension
– The obtained file name can be specified as follows:
• $cc –S file_name.i -o file_name.s
– Note: The contents of .s file are not understandable but can be
viewed
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• Assembler Stage
– Assembler converts the assembly code to an object code
(machine code) with .obj(windows) or .o(Linux) extension.
– The commands are
• $cc –c file_name.c or $cc –c file_name.i or $cc -c file_name.s
– The obtained file name can be specified as follows:
• $cc –c file_name.s –o file_name.o
– Note: The contents of object file are not understandable but
can be viewed
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• Linker Stage
– At linker stage other object files (E.g. Library Files) are linked
and an executable file with .exe(windows) or a.out(Linux) is
generated.
• Library files are pre-compiled files which can be directly linked
– Command
• $gcc file_name.c
– Note:
• Executing above command generates a file with name a.out
which is the executable format of last compiled c-program.
• Every time a new file is compiled the a.out is replaced with new
executable file
• To retain the executable content, the obtained file name can be
specified as follows $ gcc file_name.c -o file_name
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• To run the executable place ./ preceding to file_name
– $./a.out or $./file_name
• Note
– To get all the files in one shot the following command can be
used
• $gcc –save-temps file_name.c -o file_name
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Program Execution & Errors
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Editor
• Software used to create and modify source programs
– Has commands that change, delete or insert lines/characters
• Available with Assembly Language programming and High
level language programming
• Example
– Linux OS: vi, gedit, nano, pico, vim
– Windows OS: notepad
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Translators
• Software that translates the user program into the machine
readable/understandable program
• Types
– Assemblers
– Compilers
– Interpreters
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Assembler
• Software that translates Assembly language program into
Machine language program
• Reads the source program more than once
• Creates two files after translation
– Object File (Binary code of Instruction & Information about
Instruction Addresses)
– Assembler List File (Assembly language statements, Binary
code for each Instruction & Offset for each instruction)
• Types
– Self/Resident Assembler & Cross Assembler
– One-pass & Two-pass Assembler
– Meta Assembler
– Macro Assembler
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Compiler (1/6)
• Software that translates High level language program into
Machine language program
• Compiler goes through the entire program – then translates
the entire program into machine codes
• Types
– Self or Resident Compiler
– Cross Compiler
• Vs. Assembler
– A compiler is more intelligent – It checks all kinds of limits,
ranges, errors etc.
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Compiler (2/6)
Steps involved during
Compilation
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Compiler (3/6)
• Lexical Analysis or Tokenizer
– Produces Tokens from Source Code, Symbol Table and Literal
Table
• E.g. Seeing a variable, the tokenizer would generate the token
“var” and then associate the variable name (lexeme) with it in
the symbol table.
– Removes whitespace and comments.
– Handles compiler directives (i.e., as a preprocessor).
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Compiler (4/6)
• Syntactic Analysis
– Tokens are parsed to produce Parse Tree while checking that
tokens conform with the rules of the language.
– Note: Parse trees are often converted into a simplified form
known as a Syntax tree.
• E.g. Consider expression 3+4*5
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Compiler (5/6)
• Syntactic Analysis
– Tokens are parsed to produce Parse Tree while checking that
tokens conform with the rules of the language.
– Note:
• Parse trees are often converted into a simplified form known as a
Syntax tree.
• Semantic Analysis
– Produces Annotated Tree from Syntax tree.
– In addition to this, a literal table (contains information on the
strings and constants used in the program), and a symbol table
(stores information on the identifiers used in the program) are
produced by the various stages of the process.
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Compiler (6/6)
• Intermediate Code Generator & Code Optimizer
– Intermediate code generator receives input from semantic
analyzer in the form of an annotated syntax tree.
– Need of Intermediate Code Generator instead of direct
translation into target machine code?
• Intermediate code eliminates the need of a new full compiler for
every unique machine by keeping the analysis portion same for
all the compilers. The second part of compiler, synthesis, is
changed according to the target machine. It is easier to apply the
source code modifications to improve code performance by
applying code optimization techniques on the intermediate code.
• Note: Intermediate code can be either language specific or
language independent.
• Error handler
– Catch errors generated by any stages of the program.
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Interpreter
• Software that translates High level language program into
Machine language program (same as Compiler)
• Vs. Compiler
– Translates only one statement of the program at a time and
executes it. In this way it proceeds further till all the
statements are translated and executed
– A compiler is 5 to 25 times faster than an interpreter
– Compiler saves the machine codes permanently for future
reference. Interpreter does not save the machine codes
– An interpreter is a small program as compared to compiler. It
occupies less memory space, so it can be used in a smaller
system which has limited memory space
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Flow Chart (Operation of Interpreter vs. Compiler)
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Linker
• Software that links built-in functions to the System libraries
& user-defined functions to the User-defined libraries
– If linker does not find a library of a function then it informs to
compiler and then compiler generates an error
• Linker is used to combine the program modules for program
execution
– Modules: Smaller subprograms that together make a longer
program
• Compiler automatically invokes linker as the last step in
program compilation
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Locator
• Software that assigns specific addresses at which the
Executable Object code should be loaded in the System
Memory
• Example
– IBM-PC DOS has a locator called EXE2BIN
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Loader
• Software that loads machine codes (executable object code)
of a program into the system memory and prepares them for
execution
– i.e. Reads contents of executable file into memory
• Integral part of Operating System (OS)
– Once loading is complete, the OS starts the program by passing
control to the loaded program code
– In many OS, the loader is permanently resident in memory
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Software Engineering
• Definition
• Need of Paradigms
• Types
– Classical Life Cycle Model or Waterfall Model
– Iterative Model
– Rapid Application Development Model (RAD)
– Prototyping Model
– Spiral Model
– V Model
• CASE Tools
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Waterfall Model
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Software Development Life Cycle (SDLC)
• (1) Problem Statement
• (2) Requirement Gathering & Analysis
• (3) Propose Solution & Select an best feasible solution
• (4) Design
– Problem solving methods (Flow Chart, Algorithm, Pseudo Code)
• (5) Test the Design: If Test fails – Repeat from Step(4)
• (6) Coding
– Choice of Programming Lang. Paradigm – Language Selection
• (7) Test the Code: If Test fails – Repeat from Step(6)
• (8) Deployment
• (9) Maintenance
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Flow Chart
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Flow Chart Notation (1/3)
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Program Execution using Flow Chart (1/2)
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System Ready
Enter ProgramProgram Code
Edit Source Program
Compile Source
Program
C Compiler
Syntax
Errors?
A
Source Program
Object Code
B
Logic Error
Syntax Error
No Errors
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Program Execution using Flow Chart (2/2)
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System Library
Link with System
Library
Execute Object Code
Input
Data
Correct
Output
Logic &
Data
Errors?
Object Code
A
Executable Object Code
No Errors
Data Error
B
Logic Error
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Algorithm
• Algorithm
– Set of operations to be performed Step-by-step.
– Written in natural language.
– Starting from an initial state and initial input the instructions
describe a computation that, when executed, proceeds
through a finite number of well-defined successive states,
eventually producing "output" and terminating at a final
ending state.
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Example - 1
• Problem: Snakes and Ladders Game
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Problem: Snakes and Ladders Game
Flow Chart
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Example – 1 (contd.)
• Problem: Snakes and Ladders Game
– Algorithm
• (1) Game begins
• (2) Roll the dice
• (3) Move ahead as many steps as the number on the dice
– Is there a ladder? If YES, climb it & goto step 5. If NO goto step 4
• (4) Is there a snake?
– If YES, go down & goto step 6
– If NO, remain where your are & goto step 5
• (5) Have you reached End?
– If YES, You have won the game. Goto step 7
– If NO, goto step 6
• (6) Next player's turn – goto step 2
• (7) Game Over
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Example - 2
• Problem: Find Sum of two Numbers
– Algorithm
• (1) Start Operation
• (2) Declare integer variable A, B, Sum
• (3) Read two numbers A, B
• (4) Find Sum = A+B
• (5) Print Sum
• (6) End Operation
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01-Sep-2017
Problem: Finding sum of two numbers
Flow Chart Testing the Flow Chart
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Pseudocode
• Written in a format that is closely related to high level
programming language structures.
• Uses syntax common to many programming languages.
– These include standard looping structures like FOR … ENDFOR,
WHILE…ENDWHILE
– There are also some terms for standard conditional clauses like
IF-THEN … ENDIF, WHILE … ENDWHILE (this is both a loop and
a conditional clause by the way), CASE … ENDCASE
• Transforming pseudocode to programming code could be
much easier than converting an algorithm written in natural
language.
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Example
• Problem: Accept two numbers from the keyboard and
calculate the sum and product.
– Pseudocode
• Use variables sum, product, number1, number2 of type real
• Display “Input two numbers”
• Accept number1, number2
• sum = number1 + number2
• Print “The sum is “, sum
• product = number1 * number2
• Print “The Product is “, product
• End program
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Program Control Flow
• Order of Execution of Instructions
• Types
– Sequence (Default: Top to Bottom)
– Loop
• Iteration & Recursion
– Branching
• Conditional & Un-Conditional Branching or Jump
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Activity-3
• Solve the following problems with a suitable formulae/logic
and provide the design using Algorithm and Flow chart.
– (1) Find the maximum of three numbers.
– (2) Find area and circumference of a Circle.
– (3) Convert temperature into Centigrade/Fahrenheit/Kelvin.
– (4) Find Simple Interest.
– (5) Swap two numbers with/without using third variable.
– (6) Find the given number is Even or Odd.
– (7) Find the given number is Prime number or not.
– (8) Check whether the given year is Leap year or not.
– (9) Multiply two numbers without using *operator.
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Tips to Solve Activity-3
• Area = π x radius2 Circumference = π x d (d = 2r)
• °F = °C x (9/5) + 32, °C = (°F - 32) x (5/9), K = °C + 273.15
• Simple Interest = Principal x Duration x Interest Rate
• Swapping using temporary variable
– temp = a; a = b; b = temp;
• Swapping without temporary variable
– Method 1: x = x + y; y = x - y; x = x - y;
– Method 2: x = x * y; y = x / y; x = x / y;
– Method 3: x = x ^ y; y = x ^ y; x = x ^ y;
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Some Inclusions from C99
• Variables can be defined anywhere inside the function block
• New Data Types
– Boolean data type “bool” used with “stdbool.h” and “_Bool”
• Constants: “true” and “false”.
• Boolean values still behave as integers (Can be stored in integer
variables, and used anywhere integers would be valid)
– Complex data type “complex” used with “complex.h”
• Functions: creal(), cimag(), conj()
• Support to “static inline” functions
• Universal character names allows user variables to contain
other characters than the standard character set which is its
Unicode value in the form: uXXXX or UXXXXXXXX
– XXXX or XXXXXXXX - Unicode code point in hexadecimal notation
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Inclusions from C11
• Use of Anonymous Structure and Anonymous Union when
nested inside another structure.
– i.e. Structure/Union without an Identifier
• Caution with usage of gets(), deprecated in the previous C
language standard revision, ISO/IEC 9899:1999/Cor.3:2007(E)
– Using gets() may lead to buffer overflow. Hence, fgets() and
gets_s() are preferred.
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Peep into the next Module
• Programming using C Language - I
– Programming Fundamentals
– Literals & Variables
– Data Types & Modifiers
– Qualifiers & Constants
– Storage Class Specifiers
– Operators & Expressions
– Data Type Conversions
– Loops & Decision Making
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