Transcript Working with Arrays

Len Kamerman
Instructor
CS-10001, Mohawk College, Fall 2010
What Is An Array?
Using Arrays With GML
When Are They Useful?
A Sample
Give Yourself Arrays (sample problem)
An array is a COLLECTION of data items
Most variables hold a SINGLE value
“Apple”
True
One array can hold MULTIPLE values
“Apple”
380
“Cherry”
27
“Grape”
60
217
380
Arrays follow variable naming rules
But they also have an INDEX
The INDEX refers to a particular value in the
array
FruitNames
Indexes ->
0
1
2
“Apple”
“Cherry”
“Grape”
If a regular variable is like a house…
Then an array is like a condo…
They all share one common address
(variable name) but they each have their
own apartment number (an INDEX)
NOTE: the first INDEX is 0, not 1
This is the case is most programming languages!
FruitNames
Indexes ->
0
1
2
“Apple”
“Cherry”
“Grape”
In GML, you do not need to declare arrays
An array in GML looks like this:
VarName[index]
VarName is the variable name
index is an integer
Examples:
strSubject[0] = “History”;
strSubject[1] = “Math”;
Create a script in GML
Create an array with three values:
strPop[0] = “Pepsi”;
strPop[1] = “7-Up”;
strPop[2] = “Dr. Pepper”;
Print each to the screen with a message box:
show_message(strPop[0]);
show_message(strPop[1]);
show_message(strPop[2]);
When you’d like to store similar related values
strCookie[0] = “Chocolate Chip”;
strCookie[1] = “Oatmeal”;
strCookie[2] = “Anchovy”;
strCookie[3] = “Peanut Butter”;
When you need to store many values
var num1, num2, num3, num4, num5, num6,
num7, num8, num9, num10, num11……
num[0] = 7;
num[1] = 5;
num[2] = 6;
…
num[10] = 4;
Process multiple values within a REPITITION
structure (if you like loops, you’ll love arrays!)
With the use of a counter, each iteration
processes the next value
x[0] = 1;
x[1] = 7;
x[2] = 4;
for (i = 0; i < 3; i++)
{
total = total + x[i];
}
Using our same array of brands/kinds of pop:
strPop[0] = “Pepsi”;
strPop[1] = “7-Up”;
strPop[2] = “Dr. Pepper”;
for (i = 0; i < 3; i = i + 1)
{
show_message(strPop[i]);
}
Have the user enter as many numbers as they like
When they want to quit entering numbers, they enter -99
After they finish entering numbers:
show them all the numbers they entered
determine which number is the biggest and display it
var user_number, numbers, counter, biggest;
user_number = get_integer(“Enter a number”, 0);
biggest = 0;
counter = 0;
while (user_number != -99)
{
numbers[counter] = user_number;
counter = counter + 1;
user_number = get_integer(“Enter a number”, 0);
}
for (i = 0; I < counter; I = I + 1)
{
show_message(string(numbers[i]));
if (numbers[i] > biggest)
biggest = numbers[i];
}
show_message(string(biggest) + “ was the largest number”);
Prompt the user for three numbers and store them
in an array
Use a loop to put the numbers together in a string
E.g., if your numbers are 12, 57, and 42, combine
them into a string to give “125742”
Display this string in a message box
Write a script to ask the user for a lunch order
Prompt them to enter each item, for example:
hotdog
chips
Coke
When they are done entering items, they
should enter the word “nothing”
Display each item in their lunch order in the
reverse order they entered them