36. Reeborg’s diary

Click on the World button at the top to hide Reeborg’s world; click also on the Diary button to reveal Reeborg’s diary, the place where our favourite robot writes.

Have Reeborg execute the following program:

write(42);

You should see that Reeborg wrote the answer to the ultimate question about life, the universe and everything [1] in his diary.

[1]	At least according to The Hitchhiker’s guide to the Galaxy

36.1. Writing text

Note

The function write below is specific to Reeborg’s World.

In programming terms, a character is any letter, number or symbol that can be printed and a string of characters, or simply string, is any combination of character that can be printed. For example, try the following:

write("Hello world!");
write('Hello again.');

Note that the quotes that surround the string have to be the same, either double quotes like ”, or single quotes like ‘. To have a string that contains some quote characters, we can either surround it by quotes of a different type or use the escape character \:

write("Let's go.");
write('Let\'s go.');

We can combine strings using the + symbol:

write("Goodbye! " + "And thanks for all the fish.");

We can also start on a new line using the following escape sequence: \n:

write("Thank you. \nTry again");

Try it!

Make sure you try to run the above code samples or some similar.

36.2. Reeborg knows mathematics

Try this!

Try running the following program and look at the output in Reeborg’s diary.

write( 2 + 3 );  // adding numbers
write( 2 * 3 );  // multiplying numbers
write( 3 - 2 );  // subtracting numbers
write( 6 / 2 );  // dividing numbers
write( 1 + 3 * 2 ); // multiplication is done before addition
write( (1 + 3) * 2 );  // using parentheses to change normal order of operations

36.3. Using variables

We have already seen the var keyword. Let’s use it again as explore mathematical operations some more:

var length, width, area;
length = 4;
width = 6;
area = length * width;  // area of a rectangle
write(area);  // will output 24

Try it!

Make up your own examples and run them.

36.4. A word of caution

Warning

Combining strings and numbers can yield unexpected results:

write("2" + 2);

Important

The character “2” is not the same as the number 2.

Finally, note that spaces around operators, like +, are ignored by Javascript; however they often make a program easier to read for humans.