C++ decision making statements

Definition:-

Decision making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Following is the general form of a typical decision making structure found in most of the programming languages −

C++ programming language provides following types of decision making statements.

Sr.No	Statement & Description
1	if statement An ‘if’ statement consists of a boolean expression followed by one or more statements.
2	if...else statement An ‘if’ statement can be followed by an optional ‘else’ statement, which executes when the boolean expression is false.
3	switch statement A ‘switch’ statement allows a variable to be tested for equality against a list of values.
4	nested if statements You can use one ‘if’ or ‘else if’ statement inside another ‘if’ or ‘else if’ statement(s).
5	nested switch statements You can use one ‘switch’ statement inside another ‘switch’ statement(s).

 

The ? : Operator:-

We have covered conditional operator “? :” in previous chapter which can be used to replace if...else statements. It has the following general form −

Exp1 ? Exp2 : Exp3;

Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon.

The value of a ‘?’ expression is determined like this: Exp1 is evaluated. If it is true, then Exp2 is evaluated and becomes the value of the entire ‘?’ expression. If Exp1 is false, then Exp3 is evaluated and its value becomes the value of the expression.

Thank You!

C++ Constants/Literals

Definition:-

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 −

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 –

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 −

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 −

·        A value of true representing true.

·        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 −

Escape sequence	Meaning
\\	\ character
\'	' character
\"	" character
\?	? character
\a	Alert or bell
\b	Backspace
\f	Form feed
\n	Newline
\r	Carriage return
\t	Horizontal tab
\v	Vertical tab
\ooo	Octal number of one to three digits
\xhh . . .	Hexadecimal number of one or more digits

INPUT:-

#include <iostream>

using namespace std;

int main() {

   cout << "Hello\tWorld\n\n";

   return 0;

}

When the above code is compiled and executed,

OUTPUT:-

Hello   World

Defining Constants:-

There are two simple ways in C++ to define constants −

·        Using #define preprocessor.

·        Using const keyword.

The #define Preprocessor:-

Following is the form to use #define preprocessor to define a constant −

INPUT:-

#include <iostream>

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.

OUTPUT:-

50

The const Keyword:-

You can use const prefix to declare constants with a specific type as follows −

INPUT:-

#include <iostream>

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,

OUTPUT:-

50

Thank You!

Variable Types

Definition:-

A variable provides us with named storage that our programs can manipulate. Each variable in C++ has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because C++ is case-sensitive −

Sr.No	Type & Description
1	bool Stores either value true or false.
2	char Typically a single octet (one byte). This is an integer type.
3	int The most natural size of integer for the machine.
4	float A single-precision floating point value.
5	double A double-precision floating point value.
6	void Represents the absence of type.
7	wchar_t A wide character type.

C++ also allows to define various other types of variables, which we will cover in subsequent chapters like Enumeration, Pointer, Array, Reference, Data structures, and Classes.

Following section will cover how to define, declare and use various types of variables.

Type must be a valid C++ data type including char, w_char, int, float, double, bool or any user-defined object, etc., and variable_list may consist of one or more identifier names separated by commas. Some valid declarations are shown here −

int    i, j, k;

char   c, ch;

float  f, salary;

double d;

The line int i, j, k; both declares and defines the variables i, j and k; which instructs the compiler to create variables named i, j and k of type int.

Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as follows −

type variable_name = value;

Some examples are −

extern int d = 3, f = 5;    // declaration of d and f. 

int d = 3, f = 5;           // definition and initializing d and f. 

byte z = 22;                // definition and initializes z. 

char x = 'x';               // the variable x has the value 'x'.

Variable Declaration in C++:-

A variable declaration provides assurance to the compiler that there is one variable existing with the given type and name so that compiler proceed for further compilation without needing complete detail about the variable. A variable declaration has its meaning at the time of compilation only, compiler needs actual variable definition at the time of linking of the program.

A variable declaration is useful when you are using multiple files and you define your variable in one of the files which will be available at the time of linking of the program. You will use extern keyword to declare a variable at any place. Though you can declare a variable multiple times in your C++ program, but it can be defined only once in a file, a function or a block of code.

Example

Try the following example where a variable has been declared at the top, but it has been defined inside the main function –

INPUT:-

#include <iostream>

using namespace std;

// Variable declaration:

extern int a, b;

extern int c;

extern float f;

 

int main () {

   // Variable definition:

   int a, b;

   int c;

   float f;

   // actual initialization

   a = 10;

   b = 20;

   c = a + b;

   cout << c << endl ;

   f = 70.0/3.0;

   cout << f << endl ;

return 0;

}

OUTPUT:-

30

23.3333

Thank You!