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Chapter No#
Variable Scope in C++
A scope is a region of the program and broadly speaking there are three places, where variables can be declared โ ๏ท Inside a function or a block which is called local variables, ๏ท In the definition of function parameters which is called formal parameters. ๏ท Outside of all functions which is called global variables. We will learn, what is a function and it's parameter in subsequent chapters. Here let us explain what are local and global variables.
Local Variables
Variables that are declared inside a function or block are local variables. They can be used only by statements that are inside that function or block of code. Local variables are not known to functions outside their own. Following is the example using local variables โ #include using namespace std; int main () { // Local variable declaration: int a, b; int c; // actual initialization a = 10 ; b = 20 ; c = a + b; cout << c; return 0 ; }
Global Variables
Global variables are defined outside of all the functions, usually on top of the program. The global variables will hold their value throughout the life-time of your program. A global variable can be accessed by any function. That is, a global variable is available for use throughout your entire program after its declaration. Following is the example using global and local variables โ #include using namespace std; // Global variable declaration: int g; int main () { // Local variable declaration: int a, b; // actual initialization a = 10 ; b = 20 ; g = a + b; cout << g; return 0 ; } A program can have same name for local and global variables but value of local variable inside a function will take preference. For example โ #include using namespace std; // Global variable declaration: int g = 20 ; int main () { // Local variable declaration: int g = 10 ; cout << g; return 0 ; } When the above code is compiled and executed, it produces the following result โ 10
Constants/Literals in C++
Constants refer to fixed values that the program may not alter and they are called literals. Constants can be of any of the basic data types and can be divided into Integer Numerals, Floating-Point Numerals, Characters, Strings and Boolean Values. Again, constants are treated just like regular variables except that their values cannot be modified after their definition.
Integer Literals
An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal. An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order. Here are some examples of integer literals โ 212 // Legal 215u // Legal 0xFeeL // Legal 078 // Illegal: 8 is not an octal digit 032UU // Illegal: cannot repeat a suffix Following are other examples of various types of Integer literals โ 85 // decimal 0213 // octal 0x4b // hexadecimal 30 // int 30u // unsigned int 30l // long 30ul // unsigned long
Floating-point Literals
A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form. While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form, you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E. Here are some examples of floating-point literals โ 3.14159 // Legal 314159E-5L // Legal 510E // Illegal: incomplete exponent 210f // Illegal: no decimal or exponent .e55 // Illegal: missing integer or fraction
Boolean Literals
There are two Boolean literals and they are part of standard C++ keywords โ ๏ท A value of true representing true. ๏ท A value of false representing false. You should not consider the value of true equal to 1 and value of false equal to 0.
Character Literals
Character literals are enclosed in single quotes. If the literal begins with L (uppercase only), it is a wide character literal (e.g., L'x') and should be stored in wchar_t type of variable.Otherwise, it is a narrow character literal (e.g., 'x') and can be stored in a simple variable of char type. A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0'). There are certain characters in C++ when they are preceded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here, you have a list of some of such escape sequence codes โ Escape sequence Meaning \ \ character ' ' character " " character ?? character \a Alert or bell \b Backspace \f Form feed \n Newline \r Carriage return
The #define Preprocessor
Following is the form to use #define preprocessor to define a constant โ #define identifier value Following example explains it in detail โ #include using namespace std; #define LENGTH 10 #define WIDTH 5 #define NEWLINE '\n' int main() { int area; area = LENGTH * WIDTH; cout << area; cout << NEWLINE; return 0 ; } When the above code is compiled and executed, it produces the following result โ 50
The const Keyword
You can use const prefix to declare constants with a specific type as follows โ const type variable = value; Following example explains it in detail โ #include using namespace std; int main() { const int LENGTH = 10 ; const int WIDTH = 5 ; const char NEWLINE = '\n'; int area; area = LENGTH * WIDTH; cout << area; cout << NEWLINE; return 0 ; } When the above code is compiled and executed, it produces the following result โ
Note that it is a good programming practice to define constants in CAPITALS.
