1. EECE.2160 ECE Application Programming
Instructors:
Dr. Lin Li & Dr. Michael Geiger
Spring 2019
Lecture 29
Structures (continued)

2. ECE Application Programming: Lecture 29
Lecture outline
Announcements/reminders
Program 7 due Wed, 4/24
Remaining programs
Program 8 to be due Friday, 5/3 (last day of classes)
Program 9 (extra credit) to be due during finals; will not accept late submissions
Today’s lecture
Program 7 overview
Review structures basics
Structures as function arguments—examples
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ECE Application Programming: Lecture 29

3. ECE Application Programming: Lecture 29
Program 7 overview
New topics covered in this program
2-D arrays
Strings
Program accepts single-word commands
Store command as string
Display/modify state of 21 x 51 “pixel” grid
Stored as 2-D array of characters (NOT strings)
1 “pixel” = 1 char
Axis labels not stored in array (unless you modify starter file)
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ECE Application Programming: Lecture 29

4. ECE Application Programming: Lecture 29
Program 7 commands
add: Add box to grid
Prompt user for x, y coordinates of lower left corner as well as width/height
print: Print current grid state with all boxes
reset: Remove all boxes from grid and reset to initial state
exit: End the program
If user enters any other command, print an error message
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ECE Application Programming: Lecture 29

5. Program 7: initial grid state
Grid uses +, -, |, and space characters
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ECE Application Programming: Lecture 29

6. ECE Application Programming: Lecture 29
Program 7: grid + boxes
Boxes shown
11 x 8 at (10, 5)
3 x 3 at (25, 10)
4 x 1 at (36, 6)
4 x 4 at (49, 19)
Last box is partially outside grid!
Not an error, but definitely condition to account for
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ECE Application Programming: Lecture 29

7. ECE Application Programming: Lecture 29
Review: Structures
User-defined types; example:
typedef struct {
char first[50];
char middle;
char last[50];
unsigned int ID;
double GPA;
} StudentInfo;
Can define variables of that type
Scalar: StudentInfo student1;
Array: StudentInfo classList[10];
Pointer: StudentInfo *sPtr = &student1;
Access members using
Dot operator: student1.middle = ‘J’;
Arrow (if pointers): sPtr->GPA = 3.5;
Typically passed to functions by address
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ECE Application Programming: Lecture 29

8. Working with structures
Can rarely work with entire structure
Assignment only—that’s it
Work with individual member(s)
Must eventually deal with built-in types
Different modes of access for
Single structure variable  dot operator
Pointer to structure variable  arrow operator
Let’s discuss how and why …
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ECE Application Programming: Lecture 29

9. ECE Application Programming: Lecture 29
Structures vs. Arrays
Arrays
Pro: simple access (location- or index-based)
Con: doesn’t support multiple data types
Structures
Pro: more flexibility in data types
Con: complex access to members (name-based)
Complexity of access due to memory layout
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ECE Application Programming: Lecture 29

10. ECE Application Programming: Lecture 29
Dot operator
Used with single structure variable
Must specify specific instance of new data type
General form: <var name>.<member name>
Examples (to be handwritten):
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ECE Application Programming: Lecture 29

11. ECE Application Programming: Lecture 29
Pointers
Why are pointers useful?
Primarily as pointer arguments
Allow function to modify data declared outside
Why else are structure pointers useful?
Hint: how are arrays always passed to functions?
Saves time and space to pass structs by address
Use arrow operator—does work of
Pointer dereferencing
Member selection (dot operator)
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ECE Application Programming: Lecture 29

12. Structures and functions
Can pass structures to functions
int f(StudentInfo s);
Structures consume significant memory
Usually much more efficient to simply pass pointer
int g(StudentInfo *p);
Access structure through pointer: -> operator
Handles dereferencing and field access
Example: p->GPA = 3.0;
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ECE Application Programming: Lecture 29

13. Example: Structures and functions
Write the following functions that use the StudentInfo structure
Given a pointer to a single StudentInfo variable, print all of the student info to the screen using the following format:
Michael J. Geiger
ID #
GPA: 1.23
Given an array of StudentInfo variables and the size of the array, compute and return the average GPA of all students in the list
Prompt the user to enter 3 lines of input (using the format below), read the appropriate values into StudentInfo elements, and return a value of type StudentInfo
Format (user input underlined)
Enter name: Michael J. Geiger
Enter ID #:
Enter GPA: 1.23
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ECE Application Programming: Lecture 29

14. ECE Application Programming: Lecture 29
Example solution
void printStudent(StudentInfo *s) { printf(“%s %c. %s\n”, s->first, s->middle, s->last); printf(“ID #%u\n”, s->ID); printf(“GPA %.2lf\n”, s->GPA); }
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ECE Application Programming: Lecture 29

15. Example solution (cont.)
double avgGPA(StudentInfo list[], int n) { int i; double sum = 0; for (i = 0; i < n; i++) sum += list[i].GPA; return sum / n; }
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ECE Application Programming: Lecture 29

16. Example solution (cont.)
StudentInfo readStudent() { StudentInfo s; printf(“Enter name: ”); scanf(“%s %c. %s”, s.first, &s.middle, s.last); printf(“Enter ID #: ”); scanf(“%u”, &s.ID); printf(“Enter GPA: ”); scanf(“%lf”, &s.GPA); return s; }
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ECE Application Programming: Lecture 29

17. ECE Application Programming: Lecture 29
Final notes
Next time
Nested structures
Reminders:
Program 7 due Wed, 4/24
Remaining programs
Program 8 to be due Friday, 5/3 (last day of classes)
Program 9 (extra credit) to be due during finals; will not accept late submissions
6/22/2019
ECE Application Programming: Lecture 29