APS105

1. APS105 Arrays

2. Collecting Elements • How to collect elements of the same type? • Eg: ., marks on assignments: • Eg: a solution in math: x1, x2, x3, x4, x5, x6 • Eg: a (bad) solution in C: int mark1, mark2, mark3, mark4, mark5, mark6; • not very efficient, can’t manipulate marks in a loop • Awkward to add more marks a better solution: arrays!

3. Declaring and Initializing Arrays

4. Declaring an Array in C • General form: <type> <identifier>[<size>]; • Example: .

5. Initializing Arrays • General form: <type> <identifier>[] = {<value_list>}; • Examples: .

6. Init. Arrays with Length and Values • if length is greater than number of values: • remaining values default to zeros • if length is less than number of values: • error message (from the compiler) • Examples: .

7. An array with indices starting at 1 • C always starts arrays at index 0 • but sometimes this is inconvenient • or makes our code harder to read • Solution: • waste some entries to allow better indexing • Example: store t1=0.5,t2=0.25,t3=0.125 .

8. Manipulating Arrays

9. Maniuplating Arrays #define MAX 10 double list[MAX]; // set all elements to 1.0 .

10. Maniuplating Arrays #define MAX 10 double list[MAX]; // sum all the elements .

11. Maniuplating Arrays • Given an array: • Write a program to reverse the order of elements

12. Maniuplating Arrays double list[MAX]; // reverse the order of elements .

13. Arrays as Pointers

14. Array Identifiers as Pointers • Consider: int x[] = {9,7,2}; . Memory

15. Array Identifiers as Arguments • Since array identifiers are really pointers • can now easily pass an array as an argument • Example: .

16. Example: Swap • write a function to swap two array locations . Memory

17. Array Parameters and Size • Passing an array as a param gives no size • hence the function does not know array size • if needed, array size must be passed separately • Example: a function that sums an array: .