Basics of for Loops

A for loop executes a block of statements multiple times.
[Run the program]

A statement block is a group of statements enclosed inside braces {}. Braces are also called “curly brackets”.

A for loop iterates, or repeats, the execution of a statement block.

In this example, the for loop will iterate 7 times.

The sleepMs(600) statement slows down the program's execution.

Exercises:

1. In the source code, the sleepMs statement has an argument of 600. Change this argument to 150 to see how it affects the program's speed.
   [Run the program]

2. Change the argument in the sleepMs statement to 900.
   [Run the program]

This example shows the value of the loop control variable i in each iteration.
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• A for statement must not end with a semicolon, because it is a block-ended statement.

The statement sleepMs(500) pauses execution for exactly half of a second.

Exercise:

1. Modify the program to print out the numbers from 1 to 30.

The loop control variable m holds the current iteration number.

The program completes execution almost instantly because it has no delays.
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Exercise:

1. Modify the println statement to: println "m*3 = ", m*3;

In this example, the body of the for loop contains three statements inside a statement block.
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This program uses two keywords: for and println. Keywords are colored in blue.

In contrast, procedure names are not colored. Procedures use arguments inside parentheses.

The argument of the sleepMs procedure is 500 milliseconds, which is half a second.

Exercise:

1. Inside the for loop body, add the statement: println i;

In this example, the loop control variable is named k.
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The variable k is used in the expression k*3.

A variable name is a primary expression. Primary expressions can be combined to form more complex expressions.

Numbers, like 3, are also primary expressions. In this example, the number 3 is a part of the compound expression k*3.

Exercises:

1. Add this statement at the end of the source code (below the loop body): println "Program ends"; [Run the program]

2. Insert this statement inside the for loop body: sleepMs(200); [Run the program]

This example prints out the first 10 multiples of number 3.
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A string is a text, a sequence of characters, which may include letters, digits, spaces, punctuation, and other kinds of characters.

A single quote is a character called “an apostrophe”. A double quote character is more precisely called “a quotation mark”.

Strings can be enclosed in single quotes and then they may contain double quotes.

An empty println statement creates an empty line by advancing to the next line.

Exercise:

1. Modify the program so that it prints out the first ten multiples of number 7.
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2. Rename the variable i to z.
[Run the program]

Name of a variable can be composed of any letters, but it cannot contain spaces.
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A println statement scrolls the screen up when the screen is full.

This program calculates and prints the squares of the first 50 natural numbers. The square of a number is the result of multiplying the number by itself.

Exercise:

Modify the program so that it outputs the results of the expression 1000/number.

Remember to keep the arguments in the println statement separated by commas (,).

If you're stuck, you can peek at the solution.

Many different solutions are possible. Here's one example:

    println 1000, "/", number, " = ", 1000/number;

In this example, the for loop counts down from 50 to 1. The initial value (50) of the loop is greater than the bounding value (1).
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Exercise:

1. Change the argument in the sleepMs statement from 55 to the expression n*4 .

In this example, the loop control variable n increases by 3 in each iteration. This is because the step of the for loop is set to 3.
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The step of the for loop is specified after the symbols += .

If a loop is counting downwards, then the step should be specified after the symbols -= .

Exercise:

1. Change the loop so that the variable n starts from 50 and then decreases by 3 in each iteration.

for #n= 50 .. 1  -=3

This example uses some advanced features of colors and println statements that will be explained later.
[Run the program]

Exercise:

1. A string is a sequence of characters. Change the string “ZedLX” displayed on the screen to something else.

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