Nuances of working with a conditional statement

1. Sequence of if statements

Sometimes a program needs to perform many different actions depending on the value of a variable or the value of an expression.

Let's say our task is something like this:

• If the temperature is greater than 20 degrees, then put on a shirt
• If the temperature is greater than 10 degrees and less than (or equal to) 20, then put on a sweater
• If the temperature is greater than 0 degrees and less than (or equal to) 10, then put on a raincoat
• If the temperature is less than 0 degrees, then put on a coat.

Here's how this can be represented in code:

int temperature = 9;

if (temperature > 20)
   System.out.println("put on a shirt");
else // Here the temperature is less than (or equal to) 20
{
   if (temperature > 10)
      System.out.println("put on a sweater");
   else // Here the temperature is less than (or equal to) 10
   {
      if (temperature > 0)
         System.out.println("put on a raincoat");
      else // Here the temperature is less than 0
         System.out.println("put on a coat");
   }
}

If-else statements can be nested within one another. This makes it possible to implement rather complex logic in a program.

But the above example is also interesting in that we can make the code a little simpler by omitting the curly braces:

int temperature = 9;

if (temperature > 20)
   System.out.println("put on a shirt");
else // Here the temperature is less than (or equal to) 20
   if (temperature > 10)
      System.out.println("put on a sweater");
   else // Here the temperature is less than (or equal to) 10
      if (temperature > 0)
         System.out.println("put on a raincoat");
      else // Here the temperature is less than 0
         System.out.println("put on a coat");

However, programmers usually write this construct a little differently:

int temperature = 9;

if (temperature > 20)
   System.out.println("put on a shirt");
else if (temperature > 10) // Here the temperature is less than (or equal to) 20
   System.out.println("put on a sweater");
else if (temperature > 0) // Here the temperature is less than (or equal to) 10
   System.out.println("put on a raincoat");
else // Here the temperature is less than 0
   System.out.println("put on a coat");

All three of these examples are equivalent.

2. Nuances of the else block

Example:

int age = 65;

if (age < 60)
   if (age > 20)
      System.out.println("You must work");
else
   System.out.println("You don't have to work");

int age = 65;

if (age < 60)
{
   if (age > 20)
     System.out.println("You must work");
   else
     System.out.println("You don't have to work");
}

If you look at the code on the left, it seems that the screen output will be "You don't have to work". But that isn't the case. In reality, the else block and the "You don't have to work" statement are associated with the second (the closer) if statement.

In the code on the right, the associated if and else are highlighted in red. Additionally, the curly braces are placed unambiguously, clearly showing what actions will be performed. Is the string You don't have to work never displayed when age is greater than 60?

3

Task

New Java Syntax, level 3, lesson 4

Locked

This age doesn't work for me…

Think about what the program is doing. Fix the programming error so that person.age changes value. Hint: carefully review the adjustAge method

Open

3. Example of using an if-else statement

Since we explored the if-else statement so well, let's give an example:

import java.util.Scanner;
public class Solution {
   public static void main(String[] args)
   {
     Scanner console = new Scanner(System.in); // Create a Scanner object
     int a = console.nextInt(); // Read the first number from the keyboard
     int b = console.nextInt(); // Read the second number from the keyboard
     if (a < b)                   // If a is less than b
       System.out.println(a);     // we display a
     else                         // otherwise
       System.out.println(b);     // we display b
   }
}

3

Task

New Java Syntax, level 3, lesson 4

Locked

Price of apples

Calculate the total cost of apples. The total cost of apples corresponds to public static int applePrice.

Open