1. Lecture 2 Fall 2011 September 13-15, 2011 Ghufran AhmedCP
Lecture 2
Fall 2011
September 13-15, 2011
Ghufran Ahmed

2. Basics Comments in C/C++ Preprocessor Directives Name Spaces
Header Files
Program Entry Point
Return Type

3. Basics … Programming Practices Identifiers Keywords Constants
Variables
Algorithms
Expressions
Statements

4. Basic C++ Program Structure
/**********************************************************
* Header Comments
**********************************************************/
pre-processor directives
global declarations
int main() {
declarations and executable statements
return 0;
}//end block of main
// comments required by some organizations!

5. #include <iostream.h> //declares standard I/O library
/*****************************************************
* Sum two numbers
******************************************************/
#include <iostream.h> //declares standard I/O library
int main() //must have one and only one function named main {
int number1, number2; //declare two integer variables
cout << “enter two integers” << endl; //prompt for input
cin >> number1 >> number2; //input values for two variables from keyboard
cout << number1 + number2; //output sum of two numbers to the screen
return 0;
}//end block of main

6. Our First C++ Program Enter this program, then compile and run it. */
/* Program #1 - A first C++ program.
Enter this program, then compile and run it. */
#include <iostream.h>
// main() is where program execution begins.
int main() {
cout << “Hello, world!";
return 0; }
Write on the blackboard too.

7. Dissection of Program Comments have two forms in C++
//Single line comments
/*Multi-line comments*/
/* Program #1 - A first C++ program.
Enter this program, then compile and run it. */
This is a comment (C style)
Ignored by the compiler i.e. can write anything and the compiler won’t see it at all
Multiline or single or mixed with code.
Why use comments?

8. Dissection of Program C++ style comment
// main() is where program execution begins.
C++ style comment
Compiler ignores the whole line
If multiline comments, use // on each line

9. Dissection of Program
int main() {
program statements
return 0; }
Every C++ program has to have this Function; execution begins here even if other functions there; operating system calls main( ) and main returns to it
int means returns an integer;
() means takes no arguments;
{…} signify start and end of function
Variations on it e.g. main( ); int main(void); and more

10. Dissection of Program
cout << “Hello, world!";
Think of cout as the monitor screen (console output)
<< gives direction of data; Put to or Insertion operator
Prints the entire string within quotes to the screen
This whole line is a statement
C/C++ Statement
that ends with a ;

11. Dissection of Program
#include <iostream>
Tells preprocessor to include contents of the text file iostream with your source code before compiling
iostream has details about things that handle input and output e.g. cout
iostream is called an include file or header file
This is called an include directive or preprocessor directive
Can also use <iostream.h>; then no need to use the namespace construct on the next slide. Older version

12. Dissection of Program using namespace std;
Namespaces are regions where your function and variable names are recognized
The standard library is defined in a namespace called std. E.g. cout part of std namespace; similarly all others in iostream
Two functions with same names = confused compiler
Declare each in its own namespace
namespacemale::naseem
namespacefemale::naseem
std::cout Or mynamespace::cout

13. #include files <filename.h> //Standard C library header file
<filename> //Standard C++ library files
Files found in the directory defined by the INCLUDE environment variable
“myfile.h” //Your files
Files found in the current directory

14. Simple I/O cin cout streams input from standard input
uses the >> operator
(input operator, stream extraction operator)
cout
streams output to standard output
uses the << operator
(output operator, stream insertion operator)

15. Algorithms
A series of instructions in a specific order leading to a solution
Analogous to recipe, directions, procedure, routine
Anyone knows the origin of the word Algorithm?
Ninth century Persian mathematician and astronomer Al-Khowarizmi
Algebra also derived from the name of his book.

16. Rise&Shine Algorithm Any comments? Get out of bed Take off pajamas
Take a shower
Get dressed
Eat breakfast
Carpool to work
Any comments?

17. A Variation of Rise&Shine
Get out of bed
Take off pajamas
Get dressed
Take a shower
Eat breakfast
Carpool to work
Any comments?