Brief Tutorial on Coral

This tutorial teaches constructs of Coral: An ultra-simple language for learning programming. A free web-based simulator executes Coral. See corallanguage.org for more.

This tutorial is not a full intro to programming. For that, see Fundamental Programming Concepts at zyBooks.com.

Outputting text — Hello World!

The following puts the quoted text (a string literal) to output:

Put "Hello world!" to output

Run it in the simulator: Press “Enter execution”, then “Run”. When done, “Exit execution”, change the text (like Hello to Hi), and run again. 

Variables

A variable is a memory location that holds a value. Below, integer x declares a variable named x, able to hold an integer value. Then x = 5 assigns x with the value 5.

integer x
x = 5

Run it   (Notice that x’s value changes to 5 in memory)

Each line is a statement. Only one statement per line is allowed. Each statement executes one at a time.

A variable’s name starts with a letter, then any letters, digits, or underscores. Valid: x, x2, numDogs, total_width. Invalid: 2x, num-cats, flag!

A variable may be declared to hold a floating-point value rather than an integer:

float userHeight
userHeight = 5.7

Outputting variable values

An output statement can output a variable’s value. The last statement below puts the value of numPlayers (here 5) to output. Note: numPlayers is not in quotes.

integer numPlayers
numPlayers = 5
Put "Number of players: " to output
Put numPlayers to output

Run it

Above, all output will appear on one line.  A “\n” in the string literal outputs a newline.

integer numPlayers
numPlayers = 5
Put "Number of players:\n" to output
Put numPlayers to output

Run it

Getting input

Below, the second statement gets the next value from input and assigns x with that value. (x must have been declared first.)

integer x
x = Get next input

Run it

Assignment statements

An assignment statement assigns a variable with the value of an expression. Below,  the third statement assigns x with 2 times x’s current value. If x was 4, the statement assigns x with 2 * 4, or 8.

integer x
x = Get next input
x = 2 * x
Put x to output

Run it

An assignment statement’s right side can be an arithmetic expression involving +, -, *, /, and (). Ex: x = (3 * y) + (z / 2).

Example

The program below computes the total cost of a loan given the loan amount and interest.

float loanAmount
float intRate
float totalCost
loanAmount = Get next input
intRate = Get next input
totalCost = loanAmount + (loanAmount * intRate)
Put totalCost to output

Run it (feel free to change the input values)

Branches

An if-else construct implements branching. Below, if  x < 0 is true, the first branch executes, outputting "Negative". Else, the second branch executes, outputting "Non-negative".

integer x
x = Get next input
if x < 0
   Put "Negative" to output
else
   Put "Non-negative" to output

Put "\nDone" to output

Run it

While loops

A while loop construct executes its sub-statements while its condition is true. Below, while x (gotten from input) > 0, the loop outputs x’s square.

integer x
integer xSquared

x = Get next input
while x > 0
   xSquared = x * x
   Put xSquared to output
   Put "\n" to output
   x = Get next input

Run it

For loops

A for loop construct iterates a specified number of times. The below for loop iterates with i being 0, 1, 2, 3, then 4.

integer i
for i = 0; i < 5; i = i + 1
   Put i to output
   Put " " to output

Run it

Above, i = 0 executes only once, when the for loop first executes. Then condition i < 5 is checked, and if true the sub-statements execute. After, the update i = i + 1 executes, and i < 5 is checked again; the update and check repeat until the condition is false.

Comments

Comments help a human understand code. Each comment starts with //, and must be on its own line. A comment usually describes the code below the comment.

integer i

// Count down from 10 to 0
for i = 10; i >= 0; i = i - 1
   Put i to output
   // Add a space between numbers
   Put " " to output

Arrays

An array variable holds many values rather than just one value. The number of values (size) can be set in the declaration. The size can be read as myArray.size, useful in loops iterating through the array.

integer array(5) userNums
integer i

for i = 0; i < userNums.size; i = i + 1
   userNums[i] = i * 2

for i = 0; i < userNums.size; i = i + 1
   Put userNums[i] to output

Run it

Functions

A function is a statement group callable from code. A function definition may have parameter variables and a return variable. The functions returns the return variable's last value.

If a user defines a function, the main code must then be in a main function (which is otherwise implicit).

Function FtInchToCm(float numFt, float numInch) returns float numCm
   numCm = ((numFt * 12) + numInch) * 2.54

Function Main() returns nothing
   float resultCm
   resultCm = FtInchToCm(5, 6)
   Put resultCm to output

Run it

A function without parameters has empty parentheses, like Main above. A function that doesn't return a value uses "returns nothing", like Main above.

A function call's arguments can be expressions. Ex: z = FtInchToCm(x, y + 1).

A function call may appear in an expression. Ex: z = 1.0 + FtInchToCm(5, 6).

A Put statement's item may be an expression, so a call may appear there, as below.

Function FtInchToCm(float numFt, float numInch) returns float numCm
   numCm = ((numFt * 12) + numInch) * 2.54

Function Main() returns nothing
   Put FtInchToCm(5, 6) to output

Run it

Built-in functions

Several built-in math functions exist, illustrated below.

float x
float y
x = Get next input
y = Get next input
Put SquareRoot(x) to output
Put "\n" to output
Put RaiseToPower(x, y) to output
Put "\n" to output
Put AbsoluteValue(x) to output

Run it

A built-in function generates random numbers. Each call specifies a range and returns a new random number within that range.

Put RandomNumber(0, 5) to output
Put "\n" to output
Put RandomNumber(0, 5) to output
Put "\n" to output
Put RandomNumber(0, 5) to output

Run it

So programs are reproducible, the sequence of "random" numbers is always the same for a given seed. The default seed is 0. The program above always outputs 4, 0, 1. Calling built-in function SeedRandomNumber(seed) once, typically at a program's start, with a different seed (like 8) generates a different sequence.

Link to your own example



https://coral-sim.zybooks.com