JavaScript scopes and arrays, 2D array handling

JavaScript programming constructs for arrays and 2D arrays

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. Arr ays : 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. Arr ay s -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.