C++ Conditions & Switch | C++ Programming for Beginners - Class 10 PDF Download

C++ Conditions and If Statements

C++ supports the usual logical conditions from mathematics:

• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Equal to a == b
• Not Equal to: a != b

You can use these conditions to perform different actions for different decisions.

C++ has the following conditional statements:

• Use if to specify a block of code to be executed, if a specified condition is true
• Use else to specify a block of code to be executed, if the same condition is false
• Use else if to specify a new condition to test, if the first condition is false
• Use switch to specify many alternative blocks of code to be executed

The if Statement

Use the if statement to specify a block of C++ code to be executed if a condition is true.

Syntax

if (condition) {

  // block of code to be executed if the condition is true

}

In the example below, we test two values to find out if 20 is greater than 18. If the condition is true, print some text:

Example

if (20 > 18) {

  cout << "20 is greater than 18";

}

We can also test variables:

Example

int x = 20;

int y = 18;

if (x > y) {

  cout << "x is greater than y";

}

Example explained

In the example above we use two variables, x and y, to test whether x is greater than y (using the > operator). As x is 20, and y is 18, and we know that 20 is greater than 18, we print to the screen that "x is greater than y".

C++ Else

Use the else statement to specify a block of code to be executed if the condition is false.

Syntax

if (condition) {

  // block of code to be executed if the condition is true

} else {

  // block of code to be executed if the condition is false

}

Example

int time = 20;

if (time < 18) {

  cout << "Good day.";

} else {

  cout << "Good evening.";

}

// Outputs "Good evening."

Example explained

In the example above, time (20) is greater than 18, so the condition is false. Because of this, we move on to the else condition and print to the screen "Good evening". If the time was less than 18, the program would print "Good day".

C++ Else If

Use the else if statement to specify a new condition if the first condition is false.

Syntax

if (condition1) {

  // block of code to be executed if condition1 is true

} else if (condition2) {

  // block of code to be executed if the condition1 is false and condition2 is true

} else {

  // block of code to be executed if the condition1 is false and condition2 is false

}

Example

int time = 22;

if (time < 10) {

  cout << "Good morning.";

} else if (time < 20) {

  cout << "Good day.";

} else {

  cout << "Good evening.";

}

// Outputs "Good evening."

Example explained

In the example above, time (22) is greater than 10, so the first condition is false. The next condition, in the else if statement, is also false, so we move on to the else condition since condition1 and condition2 is both false - and print to the screen "Good evening".
However, if the time was 14, our program would print "Good day."

Short Hand If...Else (Ternary Operator)

There is also a short-hand if else, which is known as the ternary operator because it consists of three operands. It can be used to replace multiple lines of code with a single line. It is often used to replace simple if else statements:

Syntax

variable = (condition) ? expressionTrue : expressionFalse;

Instead of writing:

Example

int time = 20;

if (time < 18) {

  cout << "Good day.";

} else {

  cout << "Good evening.";

}

You can simply write:
Example

int time = 20;

string result = (time < 18) ? "Good day." : "Good evening.";

cout << result;

C++ Switch Statements

Use the switch statement to select one of many code blocks to be executed.

Syntax

switch(expression) {

  case x:

    // code block

    break;

  case y:

    // code block

    break;

  default:

    // code block

}

This is how it works:

• The switch expression is evaluated once
• The value of the expression is compared with the values of each case
• If there is a match, the associated block of code is executed
• The break and default keywords are optional, and will be described later in this chapter

The example below uses the weekday number to calculate the weekday name:
Example

int day = 4;

switch (day) {

  case 1:

    cout << "Monday";

    break;

  case 2:

    cout << "Tuesday";

    break;

  case 3:

    cout << "Wednesday";

    break;

  case 4:

    cout << "Thursday";

    break;

  case 5:

    cout << "Friday";

    break;

  case 6:

    cout << "Saturday";

    break;

  case 7:

    cout << "Sunday";

    break;

}

// Outputs "Thursday" (day 4)

The break Keyword

• When C++ reaches a break keyword, it breaks out of the switch block.
• This will stop the execution of more code and case testing inside the block.
• When a match is found, and the job is done, it's time for a break. There is no need for more testing.

A break can save a lot of execution time because it "ignores" the execution of all the rest of the code in the switch block.

The default Keyword

The default keyword specifies some code to run if there is no case match:

Example

int day = 4;

switch (day) {

  case 6:

    cout << "Today is Saturday";

    break;

  case 7:

    cout << "Today is Sunday";

    break;

  default:

    cout << "Looking forward to the Weekend";

}

// Outputs "Looking forward to the Weekend"

Note: The default keyword must be used as the last statement in the switch, and it does not need a break.