C++ Condational Statements

• In everyday life, we are often making decision.if the age of the person is above 60, then discount the ticket price to 40%
• The above statement have element of decision making. E.g only if the age is above 60 reduce the       ticket by 40%. If the criteria is not matched the ticket shall not be reduced by 40%.
• This decision making process is everywhere in our daily life.

Control Structure

Everyday programming requires three control structures:

•   Sequence
•   Selection
•   Iteration

Sequence

• Executing instructions in sequence
• Working  down the pag
• C / C++ follow this sequence of control until some other is specified via return, if, while, do / while, etc.
•  Statements executed one after the other in order in which they are written    

Selection

• The statement used for decisions in C++ language is known as the ‘if statement'
• If statement has a simple structure and it helps  to choose among alternative courses of actions.

Structure of if statement

if (condition)
    statement (or group of statements);
The above statement means , if condition is true, then execute the statement or a group of statements.
Here the condition is a statement which explains the condition on which a decision will be made.

Example

 if ( the grade is greater than or equal to 60)

pass the student ;
We write the condition in parentheses, followed by a statement of group of statements to be executed.
We use braces { } to make a group (block) of a number of statements.
We put ‘{‘ before the first statement and ‘}’ after the last statement
Syntax

if (condition)

  {

      statement;

      statement;

       .

       .

      statement;

  }      
// if statement is only executed when the value is true

Example

Comparing the ages of two students. If the age of first student is greater than second, then display “ student 1 is older”

#include <iostream>

main()

{

   int age1, age2;

   age1 = 12;

   age2 = 10;

   if (age1 > age2)

     cout<<“Student1 is older:";

  }

 Realtional Operators

  Example
  Write a program in which users enter a number. If the user enter positive number, add one to the number else add two to the number.

 # include<iostream>

 main()

{

 int num, neg ,pos;

   cout<<“Please enter the no.”;

   cin>> num;

    if (num > 0)

    pos= pos +1;

    else

     neg= neg +2;

}

Conditional Operator

• Closely related to if/else structure
• ?: (Conditional Operator)
• Only ternary operator in C/C++
• Takes three operands

Operands with conditional operator form conditional expression
Operand 1– condition
Operand 2 – action if condition true
Operand 3 – action if condition false

Example

grade >= 60 ? “Passed”: “Failed”

Nested if Statements

Used for multiple conditions and take some actions accordingly to each condition. Example,
if (condition 1 )
                   Statement1
else  if (condition 2 )
            Statement2
            ...
else if (condition N )
            StatementN
else
            Statement N+1

EXACTLY 1 of these statements will be executed

Example of grades (if only)

  if (grade==‘A’)
    cout<<“Excellent”;
  if (grade==‘B’)
     cout<<“Very Good”;
  if (grade==‘C’)
     cout<<“Good”;
  if (grade==‘D’)
     cout<<“poor”;
  if (grade==‘F’)
     cout<<“Fail”;
    
‘if Statement” is computationally one of most expensive statements in program due to the fact that processor has to go through many cycles to execute them for a single decision.
To avoid this , and alternate of multiple if statements can be use of if/else statements.
//nested if/else
//printing remarks for each grade

    if (grade == ‘A’)

        cout<<“Excellent”;

    else

        if (grade == ‘B’)

            cout<<“Very Good”;

        else

            if (grade == ‘C’)

                cout<<“Good”;

            else

                if (grade == ‘D’)

                    cout<<“Poor”;

                else

                    cout<<“Failed”;

In the ‘nested if statements’ the nested else is not executed if the first if condition is true and the control goes out of the if block.

Switch Statement

Multiple- selection construct that is used in  multi decision  making in an efficient way and is easy to read and understand

Structure Switch Statement

switch (expression)

{

     case constant1:

        group of statements 1;

        break;

    case constant2:

        group of statements 2;

        break;

    .

    .

    .

    default:

        default group of statements 

}

How switch works?

switch evaluates expression and checks if it is equivalent to constant1, if it is, it executes group of statements 1 until it finds the break statement. When it finds this break statement the program jumps to the end of the switch selective structure
If expression was not equal to constant1 it will be checked against constant2. If it is equal to this, it will execute group of statements 2 until a break keyword is found, and then will jump to the end of the switch selective structure
Finally, if the value of expression did not match any of the previously specified constants (you can include as many case labels as values you want to check), the program will execute the statements included after the default: label, if it exists (since it is optional)

Example

// counting grades assigned

int aCount, bCount, cCount, dCount, fCount;

switch (grade)

{

    case ‘A’: case ‘a’:

        ++aCount;

    case ‘B’: case ‘b’:

        ++bCount;

    case ‘C’: case ‘c’:

        ++cCount;

    case ‘D’: case ‘d’:

        ++dCount;

    default:

        ++fCount;

}

break Statement

break statement causes program control to move to the first statement after the selection/ repetition structure
Switch cases would otherwise run togethe.