Programming Fundamental. Instructor Name: Lecture-2

Transcription

1 Programming Fundamental Instructor Name: Lecture-2

2 Today s Lecture What is Programming? First C++ Program Programming Errors Variables in C++ Primitive Data Types in C++ Operators in C++ Operators Precedence 2

3 What is Programming? Computer programming (often shortened to programming) is a process that leads from an original formulation of a computing problem to executable computer programs. Programming involves activities: Analysis Develop understanding Generating algorithms Verification of requirements of algorithms including their correctness and resources consumption, and Implementation of algorithms in a target programming language (C++ in our case) 3

4 First Program in C++ using namespace std; #include <conio.h> #include <iostream> main() { } cout<<" Welcome to GC University"; getch(); # is HASH and also called SHARP #include: This is a pre-processor directive. It is not part of our program; it is an instruction to the compiler. It tells the C compiler to include the contents of a file i.e. iostream. The compiler knows that it is a system file, and therefore looks for it in a special place. 4

5 First Program in C++ Namespace in C++ Different libraries may have functions or variables with same name A namespace is designed to overcome this difficulty by using additional information to differentiate similar functions, classes, variables etc. with the same name available in different libraries. Using namespace, you can define the context in which names are defined. In essence, a namespace defines a scope. A namespace definition begins with the keyword namespace followed by the namespace name as follows: namespace namespace_name; 5

6 First Program in C++ The Using Directive To call the namespace-enabled version of either function or variable, prepend the namespace name as follows: name_space::code; You can also avoid prepending of namespaces with the using namespace directive which tells the compiler that the subsequent code is making use of names in the specified namespace The using directive can also be used to refer to a particular item within a namespace. For example, using std::cout; 6

7 First Program in C++ #include directive Both user and system header files are included using the preprocessing directive #include. It has two variants: #include <file> - used for system header files. It searches for a file named file in a standard list of system directories. #include "file - used for header files of your own program. It searches for a file named file first in the directory containing the current file, then in the quote directories and then the same directories used for <file>. 7

8 First Program in C++ main() Function All C++ Must have main() function When the operating system runs a program in C, it passes control of the computer over to that program. The main() function uses its parentheses() to contain any information typed after the program name at the command prompt. This is useful for more advanced programming. The curly braces {} are used for organization. They contain programming instructions that belong to the function. Those programming instructions are how the function carries out its task or does its thing. Without main() function a C++ program will not execute. 8

9 First Program in C++ cout in C++ The predefined object cout is an instance of ostream class. The cout object is said to be "connected to" the standard output device, which usually is the display screen. The cout is used in conjunction with the stream insertion operator, which is written as << which are two less than signs indicates the direction of data cout<<" Welcome to GC University"; Thing between the double quotes ( ) is known as character string, will display it on the screen. 9

10 First Program in C++ Semicolon ; in C++ The semicolon is part of the syntax of C++. It tells the compiler that you're at the end of a command. The semicolon (;) will be used at the end of the every statement other wise compiler will report an error. The error reported as result of missing semicolon(;) is referred as syntax error 10

11 Programming Errors Three Types of Errors 1) Syntax Error Detected By the Compiler 2) Logical Error Produce incorrect result due to wrong logic 3) Runtime Error Causes the program to abort 11

12 Variables in C++ What is Variable? A variable is used to store a piece of data for processing. It is called variable because you can change the stored value with new value during program execution A variable is a named storage location, that stores a value of a particular data type 12

13 Variables in C++ Variable 13

14 Variables in C++ Dissecting a Variable In a Program a variable Consists of: Name: Used as identifier for the variable. e.g. radius, area, age Type: Represents the type of data a variable will hold. e.g. Integer, Float Size: Represents memory size a variable require to store a value. It depends on the type of variable and compiler that compiles the code. Value: Actual value that is stored in variable 14

15 Variables in C++ Variable Declaration Rule A variable must start with: Character Underscore _ (Not recommended) A variable must [recommended] Consists of sequence of Upper/lower case Characters, numbers (0-9), _ up to certain length have a name that is self-descriptive and closely reflects the meaning of the variable e.g. age, user_name, , address,ph_no not be of single character and meaning less unless they are common names like x,and z for coordinators 15

16 Variables in C++ Variable Declaration Rule It is perfectly okay to use long names of says 30 characters to make sure that the name accurately reflects its meaning! Use singular and plural nouns prudently to differentiate between singular and plural variables. For example, you may use the variable row to refer to a single row number and the variable rows to refer to many rows. 16

17 Variables in C++ Variable Declaration Rule Prohibition: White space (blank, tab, new-line) and other special characters (such as +, -, *, &, commas, etc.) are not allowed. It cannot begin with a digit. An identifier cannot be a reserved keyword or a reserved literal (e.g. int, double, if, else, for, main,while,break). Identifiers are case-sensitive. E.g. A rose is NOT a Rose, and is NOT a ROSE. 17

18 Variable Data Types Data Types While doing programming in any programming language, you need to use various variables to store various information. Variables are nothing but reserved memory locations to store values, this means variable reserve some space in memory. Information store in variables may be of various data types like character, wide character, integer, floating point, double floating point, boolean etc. Based on the data type of a variable, the operating system allocates memory and decides what can be stored in the reserved memory. A data type is set of values and operations performed on those value 18

19 Variable Data Types Primitive Data Types Integers: used to store numerical values(signed or unsigned). Characters: used to store Characters A to z. Every alphanumeric digit and or symbol encoded in single quotes in considered a character. Floating-point: used store the decimal point numbers. Boolean: A special type called bool, which takes a value of either true or false. 19

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