Java For Kids tutorial 3

Operators are special symbols used to combine variables and/or values.

The first set of Operators that we will look are maths operations such as plus, minus , multiply, divide.

Here is a simple program that uses these operators:

    void main() {
            int a = 1;
            int b = 2;
            int c = a + b;
            printLine(c);
    }

What should you get printed out?

Relational Operators compare two values to see if they are equal or one is greater or less than the other one.

The main use for the above relational operators are in CONDITIONAL phrases. Or to put it simply in “What if” situations. Lets say you were writing a program for bus fares. And you wanted to know the correct fare based on age. How would you describe this problem? Here is a way:

    IF the passenger's age is greater than 18,
    THEN the price is normal Fare.
    OTHERWISE The price is half fare.

Lets write that same algorithm (what is written above in plain english) in Java. It is a CONDITIONAL phrase.

    if (age > 18)
    {
            price = 80;
    }
    else
    {
            price = 40;
    }

OK lets write our Java program to calculate bus fares.

    void main() {
	// 1. declare variables
	int fare = 80;
	int age;
 
	// 2. get the age
	printLine("What is your age please?");
 
	// 3. the user enters their age
	age = readInt();
 
	// 4. check if over 18
	if (age>18)
	{
	    printLine("The fare will be " +
	        fare + ", thank you.");
	}
	// 5. the IF statement is false
	else
	{
	    printLine("The fare will be " +
	        fare/2 + ", thanks kid");
	}
    }

Notes on the bus fare java program

• We declare all the variables.
• We ask for the user to input (put in ) their age.
• The user enters their age. readInt() is used to assign an int value to an int variable, age.
• Then the program uses an IF statement to check if the age is greater than 18 . If this is true, then “The fare will be 80 cents, thank you” will be printed. That is, the statements inside the first curly brackets {} will be processed.
• If the if statement is false, i.e. the age is less than or equal to 18 (all other possibilities besides age > 18), THEN the statements inside the curly brackets after ELSE are processed.

Both set of statements, (if or else) cannot both be processed. Either one of them will be carried out. It is a case of EITHER OR.

    if (this statement is true)
    {
        // perform the actions inside these curly brackets
    }
    else
    {
        // if the statement after the IF is false or untrue then
        // perform the actions inside these brackets here
    }