Computer programming
Introduction
Variables and assignment
• variable are used to name and store data.
• value is any type of data held by the variable.
• Variables are implemented as Memory locations assigned by the compiler
• The value of the variable Is kept in the memory location assigned to that variable.
Identifiers
• Identifier : name of the variable
• An identifier must start with a letter or an underscore
• Other characters can be letters, digits or the underscore symbol
• C++ is a case-sensitive language;
• eg Rate | RATE | rate => are different variables
Rules for writing an identifier
1. The first letter should be either be a letter or underscore
2. Identifiers shouldn’t be keywords
Keywords or Reserved words are words that have predefined meaning in c++ and they’re
defined in the libraries.
Example: cin , cout, int, include
3. There shall be no space between words in the identifier
4. To make your program easy to understand, u should always use
meaningful names for variables.
Variable declarations
• Declaring a variable is telling the complier the kind of data to be stored in the
variable.
• For example:
int number_of_bars; => integer type
double one_weight , total_weight; => double type
• When there is more than one declarations they are separated by comma.
• Each declarations ends with a semicolon.
• All variables must be declared before use
Assignment Statements
• Assignment statement : a direct way to change the value of a
• For example:
total_weight = one_weight * number_of_bars;
• This assignment statement sets the value of total_weight to the value of one_weight multiplied by the
value of number_of_bars.
• An assignment statement always consists of
• a variable on the left-side of the equal sign
• an expression on the right-side
• ends with a semicolon.
• Example of assignment
• total_weight = one_weight;
• weight = one_weight + 3;
• A variable can be initialized at the time of declaration
• E.g. int a = 6;
2.2 Input and output
An input stream : the stream of input that is being An output stream : the stream of output generated
by the program
fed to the program
• Output using cout
• Input using cin
• Output to the screen
• Input from user
• For example
• For example
• cout << ”Please enter your name: ”;
• string firstName
• cout << “the total cost is $” << (price + tax);
cin >> firstName
• cout << first name << “ “ << second number;
• The arrow notation << is often called the
insertion operation.
INCLUDE DIRECTIVES AND NAMESPACES
#include <iostream> - These two lines make the library iostream available.
Using namespace std; - iostream library includes the definition of cin and cout and others
• C++ divides names into namespaces.
• A namespace is a collection of names, such as the names cin and cout.
• Using directive : a statement that specifies a namespace by “using”.
• i.e. using namespace std;
• This statement says that your program is using the std (standard) namespace.
Escape sequences
• The \ preceding a character tells the compiler that the character
following the \ doesn’t have the same meaning as the character itself.
• Such a sequence is called an escape sequence
Data type
• Data-types of a variable restricts the type of data to be stored on the variable at declaration.
• At variable declaration in C++, the compiler allocates memory based on the variable’s data-type
• Every data type requires a different amount of memory.
Data type
• Primitive Data Types:
• are built-in or predefined data types
• can be used directly by the user to declare variables
• Derived Data Types:
• They are derived from the primitive or built-in data types
• Abstract or User-Defined Data Types:
• are defined by user
Primitive Data type
• Integer:
• Keyword used for integer data types is int
• Integers typically requires 4 bytes of memory space
• ranges from -2147483648 to 2147483647
• Character:
• Keyword used for character data type is char
• Characters typically requires 1 byte of memory space
• ranges from -128 to 127 or 0 to 255
• Boolean:
• used for storing boolean or logical values (true or false)
• Keyword used for boolean data type is bool
Primitive Data type …
• Floating Point:
• used for storing single precision floating point values or decimal values
• Keyword used for floating point data type is float
• Float variables typically requires 4 byte of memory space
• Double Floating Point:
• used for storing double precision floating point values or decimal values
• Keyword used for double floating point data type is double
• Double variables typically requires 8 byte of memory space
• Valueless or Void:
• Void means without any value.
• void datatype represents a valueless entity.
• Void data type is used for those function which does not returns a value.
Data type Modifiers
Operators
• An operator is a symbol that tells the compiler to perform specific
mathematical or logical manipulations.
• Arithmetic Operators
• Assignment Operators
• Relational Operators
• Logical Operators
• Bitwise Operators
• Misc Operators
Operators …
Arithmetic Operators
Operators …
Assignment Operators
Operators …
Assignment Operators …
Operators …
Relational Operators
Operators …
Logical Operators
Operators …
Bitwise Operators
Operators …
Postfix vs Prefix
• Postfix - returns the value and then performs the operation
• Eg int a = 2;
• Cout <<a; => this gives out 2
• Cout<<a++; => this gives out 2
• Cout<<a; => this gives out 3
• Prefix - performs the operation and returns the value
• Eg int a = 2;
• Cout <<a; => this gives out 2
• Cout<<++a; => this gives out 3
• Cout<<a; => this gives out 3
Precedence of operators
