1. EECE.2160 ECE Application Programming
Instructor:
Dr. Michael Geiger
Spring 2019
Lecture 24
Arrays and functions

2. ECE Application Programming: Lecture 24
Lecture outline
Announcements/reminders
Program 5 due 4/5
Today’s lecture
Arrays and functions
Character arrays and strings
4/25/2019
ECE Application Programming: Lecture 24

3. Passing arrays to functions
Do not need to specify array size (for reasons I’ll explain shortly)
Compiler will actually ignore 1-D array size, even if you put it in prototype
Therefore cannot check array size inside function
Prototype typically has array name and brackets to indicate you’re dealing with array
e.g. int findAvg(int arr[ ], int n);
n = # elements in array
4/25/2019
ECE Application Programming: Lecture 24

4. ECE Application Programming: Lecture 24
Example
Write a function for each of the following
findAvg(): Given an array of doubles (arr) and the # of elements in the array (n), find the average of all array elements
findMax(): Given an array of ints (arr) and the # of elements (n), find the largest (i.e., most positive) element in the array
4/25/2019
ECE Application Programming: Lecture 24

5. Passing Arrays to functions (findAvg)
double findAvg(double arr[], int n) { int i; double sum = 0; for (i=0; i < n; i++) sum += arr[i]; return sum / n; }
4/25/2019
ECE Application Programming: Lecture 24

6. Passing Arrays to functions (findMax)
int findMax(int arr[], int n) { int i, big; big = arr[0]; for (i=1; i < n; i++) { if (arr[i] > big) big = arr[i]; } return big; }
4/25/2019
ECE Application Programming: Lecture 24

7. ECE Application Programming: Lecture 24
SclAry() function
Consider function that takes as arguments
An array
The array size
A scaling factor to add to each element
Function can’t “return” array … so is there any point to it?
4/25/2019
ECE Application Programming: Lecture 24

8. Passing Arrays to functions (SclAry)
//******************************************* // function SclAry // On Entry: // tests[] - array with values to scale // n number of values to scale // s number of points to scale // On Exit: // The first n values of tests[] are // scaled by s points void SclAry(int test[], int n, int s) { int i; for (i=0; i<n; i++) test[i]=test[i]+s; // or use test[i]+=s; }
4/25/2019
ECE Application Programming: Lecture 24

9. Passing Arrays to functions (SclAry)
#include <stdio.h> void SclAry(int test [], int n, int s); void main(void) { int i; int x[]={ 51,62,73,84,95,100,66,57,48,79 }; SclAry(x,10,10); for (i=0; i < 10; i++) printf("%d ",x[i]); printf("\n"); } void SclAry(int test[], int n, int s) { int i; for (i=0; i<n; i++) test[i]=test[i]+s; // or use test[i]+=s; }
4/25/2019
ECE Application Programming: Lecture 24

10. ECE Application Programming: Lecture 24
Passing Arrays to functions (SclAry)
Output of program:
For reference:
int x[]={ 51,62,73,84,95,100,66,57,48,79 };
Function call changed array—why?
4/25/2019
ECE Application Programming: Lecture 24

11. Passing Arrays to functions
Before call to SclAry After call to SclAry
test[0] 51
3044
test[0] 61
3044
test[1] 62
3048
test[1] 72
3048
test[2] 73
304C
test[2] 83
304C
test[3] 84
3050
test[3] 94
3050
test[4] 95
3054
test[4]
105
3054
test[5]
100
3058
test[5]
110
3058
test[6] 66
305C
test[6] 76
305C
test[7] 57
3060
test[7] 67
3060
test[8] 48
3064
test[8] 58
3064
test[9] 79
3068
test[9] 89
3068
Passing the name only (i.e. test vs. test[4]) passes the ADDRESS of element zero of the array.
Put another way: myfunc(ary) same as myfunc (&ary[0])
4/25/2019
ECE Application Programming: Lecture 24

12. ECE Application Programming: Lecture 24
Strings in C
Strings in C: null-terminated arrays of characters
“Hello”{‘H’, ‘e’, ‘l’, ‘l’, ‘o’, 0}
Null character = 0 = ‘\0’
Can declare array to hold string
Need space to hold null: char hello[5] would be too small
Can use string constants to directly initialize
char hello[] = “Hello”;
Equivalent to:
char hello[6];
hello[0] = ‘H’;
hello[1] = ‘e’;
hello[2] = ‘l’;
hello[3] = ‘l’;
hello[4] = ‘o’;
hello[5] = OR-- hello[5] = ‘\0’;
4/25/2019
ECE Application Programming: Lecture 24

13. Strings and I/O functions
Can pass string as array or pointer: char *
printf(), scanf() take char * as first argument
Given string char hello[] from previous slide:
Print directly: printf(hello);
Print w/formatting using %s: printf(“%s\n”, hello);
Print individual character: printf(“%c\n”, hello[1]);
Overwrite with new string: scanf(“%s”, hello);
Ampersand is unnecessary  array name is already address
scanf() will read up to first whitespace character
4/25/2019
ECE Application Programming: Lecture 24

14. ECE Application Programming: Lecture 24
Final notes
Next time
More on strings –or– Exam 2 Review
Reminders:
Program 5 due 4/5
4/25/2019
ECE Application Programming: Lecture 24