Lecture 9 introduces variable scope in programming, highlighting global and local variables. It discusses common errors related to variable copying, especially with simple types versus objects, and elaborates on arrays, including single-dimension and 2D arrays. The session concludes with how to use nested loops to iterate through 2D arrays and the concept of scope for variable visibility within a program.

1. Introduction to Programming I
Lecture 9

2. Variables Scope

3. Variables Scope
• Global Variables: Seen all over your codes
• Local Variables: only seen and used within the function it is
declared in

4. Variables Scope
• Global Variables:
Seen all over
your codes
• Local Variables: only
seen and used
within the function
it is declared in

5. Variables Scope

6. Common Errors with Scope

7. Copying Variables
var myVariable1 = 50;
var myVariable2 = myVariable1;
What is the value stored for myVariable2 ?
50

8. Copying Variables II
var myVariable1 = 50;
var myVariable2 = myVariable1;
myVariable2 *= 10;
What is the value stored for myVariable2 and myVariable1?
500, 50

9. Copying Variables III: Objects
rect2 = rect1;
rect2.size = rect2.size*2;
What is the size of rect1?
double the initial
size

10. Copying Variables III: Objects
-You are copying the reference to the object not the value like the simple variable
types e.g., string, Boolean, number.
- What if you want to have 2 different objects?
- Pass the simple type not the entire object

11. Arrays:
var sizes = [4, 9, 10, 5, 110, 95, 40, 40];
var names = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus",
"Neptune"];
var colours = ["grey", "brown", "blue", "red", "sienna", "pink", "blue", "cyan"];
var arrayPlanets = [planet1, planet2, planet3, planet4, planet5, planet6, planet7,
planet8];

12. Arrays: Single Dimension vs. 2D Arrays
• Array of simple variable types
• Array of objects
• Array of arrays
• 2D arrays

13. Arrays: 2D Arrays Syntax
var myArray = [];
var myArray = [[],[],[]];

14. Arrays: 2D Arrays Initialising
var myArray = [];
var my2DArray = [[],[],[]];
var my2DArray = [[1,2,3],[4,5,6],[7,8,9,10]];
console.table (my2DArray);
my2DArray [0][0];  1
my2DArray [1][2];  6

15. Looping over a 2D Array
For (var i=0; i<my2DArray.length; ++i)
for (var j=0; j<my2DArray[i].length; ++j)
console.log(my2DArray[i][j]);

16. Arrays
-You are copying the reference to the object not the value like the simple variable
types e.g., string, Boolean, number.
- What if you want to have 2 different objects?
- Pass the simple type not the entire object

17. Lecture 9: Summary
• Use the concept of scope to explain how different parts of a program see
different variables.
• Use nested loops to iterate through 2D arrays of numbers and generate
images from them.