1. EECE.2160 ECE Application Programming
Instructors:
Dr. Michael Geiger & Dr. Peilong Li
Spring 2017
Lecture 24:
Structures (cont.)

2. ECE Application Programming: Lecture 24
Lecture outline
Announcements/reminders
Program 6 due today
Exam 2 in class 3/29
Will be allowed one double-sided 8.5” x 11” note sheet
Covers material starting after Exam 1, through end of week (lectures 13-17, 19-24)
Change for late/regrade submissions & other grading issues: please directly contact TAs and CC your instructor
Li Zhou odd-numbered programs
Zhendong Wang even-numbered programs
Today’s class
Finish structures
4/12/2019
ECE Application Programming: Lecture 24

3. Review: String functions
In <string.h> library:
Copying strings:
char *strcpy(char *dest,
const char *source);
char *strncpy(char *dest,
const char *source,
size_t num);
Return dest
Does not append ‘\0’ unless length of source < num
Comparing strings:
int strcmp(const char *s1, const char *s2);
int strncmp(const char *s1, const char *s2, size_t num);
Character-by-character comparison of character values
Returns 0 if s1 == s2, >0 if s1 > s2, <0 if s1 < s2
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ECE Application Programming: Lecture 24

4. Review: String functions (cont.)
Find # of characters in a string
size_t strlen(const char *s1);
Returns # characters before ‘\0’
Not necessarily size of array
“Add” strings together—string concatenation
char *strcat(char *dest,
const char *source);
char *strncat(char *dest,
const char *source,
size_t num);
Returns dest
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ECE Application Programming: Lecture 24

5. ECE Application Programming: Lecture 24
Review: Structures
User-defined data types; collections of data with different types
Can define structure as a type using typedef
Could omit typedef, but would need “struct” before type name
Syntax: typedef struct {
<list of variables>
} <typeName>;
Example:
typedef struct {
char first[50];
char middle;
char last[50];
unsigned int ID;
double GPA;
} StudentInfo;
typedef usually at program start (with #include, #define)
<typeName> usually starts with capital letter
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ECE Application Programming: Lecture 24

6. ECE Application Programming: Lecture 24
Using structure types
Once defined, can declare variables using that type
Scalar: StudentInfo student1;
Array: StudentInfo classList[10];
Pointer: StudentInfo *sPtr;
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ECE Application Programming: Lecture 24

7. Using structure variables
Initialization very similar to array initialization:
StudentInfo student1 =
{ “John”, ‘Q’, “Smith”,
, 3.75 };
Accessing structure elements: . operator
Syntax: <var name>.<element name>
Examples:
printf(“%s %c %s”, student1.first, student1.middle, student1.last);
student1.GPA = 3.5;
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ECE Application Programming: Lecture 24

8. Example: Using structures
What does the following print?
typedef struct {
double real;
double imag;
} Complex;
int main() {
Complex a = {1, 2};
Complex b = {3.4, 5.6};
Complex c, d, e;
printf("A = %.2lf+%.2lfi\n",
a.real, a.imag);
printf("B = %.2lf+%.2lfi\n", b.real, b.imag);
c = a;
d.real = a.real + b.real;
d.imag = a.imag + b.imag;
e.real = a.real - b.real;
e.imag = a.imag - b.imag;
printf("C = %.2lf+%.2lfi\n", c.real, c.imag);
printf("D = %.2lf+%.2lfi\n", d.real, d.imag);
printf("E = %.2lf+%.2lfi\n", e.real, e.imag);
return 0; }
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ECE Application Programming: Lecture 24

9. ECE Application Programming: Lecture 24
Example solution
A = i B = i C = i D = i E = i Note: code in handout has spaces before and after ‘+’ for readability; code on previous slide doesn’t because it wouldn’t fit!
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ECE Application Programming: Lecture 24

10. 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 *s);
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ECE Application Programming: Lecture 24

11. 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 24

12. ECE Application Programming: Lecture 24
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 24

13. Example solution (cont.)
double avgGPA(StudentInfo list[], int n) { int i; int sum = 0; for (i = 0; i < n; i++) sum += list[i].GPA; return sum / n; }
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ECE Application Programming: Lecture 24

14. 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 24

15. ECE Application Programming: Lecture 24
Nested structures
Variables inside structures can be structures themselves
Example: general structure for names
typedef struct {
char first[50]; // First name
char middle; // Middle initial
char last[50]; // Last name
} Name;
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ECE Application Programming: Lecture 24

16. Nested structures (cont.)
Example (cont.): Could use Name structure any time you need name within a structure
Redefining StudentInfo:
typedef struct {
Name stu_name; // Student name
unsigned int ID; // ID #
double GPA; // Grade point
} StudentInfo;
Will need multiple dot operators to access field within nested structure
Given StudentInfo s1;
s1.stu_name  Name structure within s1
s1.stu_name.middle  middle initial of name within s1
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ECE Application Programming: Lecture 24

17. ECE Application Programming: Lecture 24
Next time
Exam 1 Preview
Reminders:
Program 6 due today
Exam 2 in class 3/29
Will be allowed one double-sided 8.5” x 11” note sheet
Covers material starting after Exam 1, through end of week (lectures 13-17, 19-24)
Change for late/regrade submissions & other grading issues: please directly contact TAs and CC your instructor
Li Zhou odd-numbered programs
Zhendong Wang even-numbered programs
4/12/2019
ECE Application Programming: Lecture 24