Arrays

1. Arrays

2. Example • Write a program to keep track of all students’ scores on quiz 1. • Need a list of everyone’s score • Declare 14 double variables? • What about next semester?

3. Arrays • Declare a list of variables – all with the same type double scores[14]; • <data type> name[size];

4. Example //declare the array scores: 90.5 73 87

5. Example //declare the array double scores[3]; //put 90.5 in the first box scores:

6. Example //declare the array double scores[3]; //put 90.5 in the first box scores[0] = 90.5; scores: 90.5

7. Example //declare the array double scores[3]; //put 90.5 in the first box scores[0] = 90.5; scores[1] = 73; scores[3] = 87; scores: 90.5 73 87

8. Alternative double scores[3] = {90.5, 73, 87}; • Initializes elements of the array to values given when array is created

9. Subscripts • Subscript describes which box of the array you are dealing with • Array of size N has subscripts • 0, 1, 2, … (n-1) • array of size 3 – 0, 1, 2 • subscript added to base address of array • Subscript can be a variable or expression which produces an integer • scores[i]; • scores[i+5]; • If subscript specified does not exist – runtime error

10. Example scores[1]; scores[3]; //assume i = -2; scores[i+2]; sum = scores[1] + scores[2]; sum = scores[1] + scores[i*8]; scores[2] = scores[1] + 6; scores: 90.5 73 87

11. Accessing Array Elements • Print all elements of the array scores • Use only one printf statement

12. Accessing Array Elements • Print all elements of the array scores • Use only one printf statement #include <stdio.h> #define MAX_SCORES 3 int main(void) { int i; double scores[MAX_SCORES] = {90.5, 72, 87}; for(i = 0; i < MAX_SCORES; i++) { printf("Score %d: %lf\n", i, scores[i]); } return(0); }

13. Passing Array Elements • Write a function to add two elements of an array

14. Passing Array Elements • Write a function to add two elements of an array • How is the function called? double add(double num1, double num2) { return (num1 + num2); }

15. Passing Array Elements • Write a function to add two elements of an array • How is the function called? add(scores[0], scores[1]); … double add(double num1, double num2) { return (num1 + num2); }

16. Passing Array Elements • Write a function to swap two elements of an array

17. Passing Array Elements • Write a function to swap two elements of an array • How do you call swap? void swap(double *num1, double *num2) { double tmp = *num1; *num1 = *num2; *num2 = tmp; }

18. Passing Array Elements • Write a function to swap two elements of an array • How do you call swap? swap(&scores[0], &scores[1]); … void swap(double *num1, double *num2) { double tmp = *num1; *num1 = *num2; *num2 = tmp; }

19. Passing Arrays • Would like to pass an entire array into a function • Sum all elements, prompt user for values • Array name is treated as a pointer (to first element of array)

20. Example add_one(scores, MAX_SCORES); void add_one(double scores_to_add[], int numscores) { int i; for(i = 0; i < MAX_SCORES; i++) { scores_to_add[i] = scores_to_add[i] + 1; } }

21. Misc • Parallel Arrays • Partially filled arrays