1. EECE.2160 ECE Application Programming
Instructors:
Dr. Michael Geiger
Summer 2017
Lecture 10
Structures
Exam 2 Preview

2. ECE Application Programming: Lecture 10
Lecture outline
Announcements/reminders
Ch. 7 activities due Thursday
Program 5 to be posted; due Wednesday 6/20
Old spec and starter files (which will become template files) on course schedule page
Exam 2: Monday, 6/18
Will be allowed one 8.5” x 11” note sheet
Covers material from Lec. 6-9 (not structures)
Today’s lecture
Structures
Exam 2 Preview
6/17/2019
ECE Application Programming: Lecture 10

3. ECE Application Programming: Lecture 10
Review: strings
Represented as character arrays
Can be initialized using string constants
char hello[] = "Hello";
Can access individual elements
hello[3] = 'l';
Can print directly or with formatting
Print directly: printf(hello);
Print w/formatting using %s: printf("%s\n", hello);
Reading strings: scanf("%s", str);
Reads all characters up to (but not including) first space, tab, or newline
Must leave enough room for terminating '\0'
6/17/2019
ECE Application Programming: Lecture 10

4. 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
strncpy() not guaranteed to add null terminator
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
6/17/2019
ECE Application Programming: Lecture 10

5. 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
strncat() guaranteed to add null terminator
6/17/2019
ECE Application Programming: Lecture 10

6. ECE Application Programming: Lecture 10
Structures
Arrays: groups of data with same type
Structures: groups of data with (potentially) different types
Example: record to store information about student:
First name (char [])
Middle initial (char)
Last name (char [])
ID # (unsigned int)
GPA (double)
Any data type—scalar, array, pointer (even other structures) allowed
6/17/2019
ECE Application Programming: Lecture 10

7. Declaring structure types
Can define structure as a type using typedef
Could omit typedef, but would need “struct” before type name
Syntax: typedef struct {
<list of members>
} <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 10

8. ECE Application Programming: Lecture 10
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 10

9. 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 10

10. 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; }
6/17/2019
ECE Application Programming: Lecture 10

11. ECE Application Programming: Lecture 10
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!
6/17/2019
ECE Application Programming: Lecture 10

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 *s);
6/17/2019
ECE Application Programming: Lecture 10

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 10

14. ECE Application Programming: Lecture 10
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); }
6/17/2019
ECE Application Programming: Lecture 10

15. 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; }
6/17/2019
ECE Application Programming: Lecture 10

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; }
6/17/2019
ECE Application Programming: Lecture 10

17. ECE Application Programming: Lecture 25
Nested structures
Structures can contain other structures:
typedef struct {
char first[50]; // First name
char middle; // Middle initial
char last[50]; // Last name
} Name;
Name sname; // Student name
unsigned int ID; // ID #
double GPA; // Grade point
} SINew;
Will need multiple dot operators to access field within nested structure
Given SINew s1;
s1.sname  Name structure within s1
s1.sname.middle  middle initial of name within s1
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ECE Application Programming: Lecture 25

18. ECE Application Programming: Lecture 10
Exam 2 notes
Allowed one 8.5” x 11” double-sided note sheet
No other notes
No electronic devices (calculator, phone, etc.)
Exam will last 2 hours and 20 minutes
Covers material starting after Exam 1, through lecture 9 (lectures 6-9)
Structures are not on Exam 2
Same general format as Exam 1
3 questions (each with multiple parts, so actually ~10 questions) + 1 extra credit question
Functions (code reading/writing, MC?)
Arrays (code reading/writing, MC?)
Strings (code reading?, MC)
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ECE Application Programming: Lecture 10

19. ECE Application Programming: Lecture 10
Review: functions
Used to break programs into smaller pieces
Useful when code sequences repeated
Functions have:
An optional return value
A name
Optional arguments
Must be prototyped or written completely prior to use
Arguments can be:
Passed by value: copy of argument is sent to function
Arguments cannot be modified outside function
Passed by address: address of argument
Use pointers or address operator (&)
Arguments can be modified outside function—used to “return” multiple values
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ECE Application Programming: Lecture 10

20. ECE Application Programming: Lecture 10
Review: pointers
Pointer: address of a variable
Can get address of existing object using &
Can get value of existing pointer using *
Can assign pointers of same type to each other
Pointer declaration:
<base type>* <pointer name>
Base type determines how reference is interpreted
Use pointers as function arguments  pass by address
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ECE Application Programming: Lecture 10

21. Review: arrays & pointers
Arrays: groups of data with same type
x[10] has 10 elements, x[0] through x[9]
Can also define with initial values
e.g. double list[] = {1.2, 0.75, };
Must be sure to access inside bounds
Array name is a pointer
Arrays are always passed by address to functions
Should pass size of array as additional argument
e.g. void f(int arr[], int n);
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ECE Application Programming: Lecture 10

22. ECE Application Programming: Lecture 10
Review: 2D arrays
Declared similarly to 1D arrays
Example (see below): int x[3][4];
Index elements similarly to 1-D arrays
Initialize: int y[3][4] =
{ {1, 2, 3, 4},
{5, 6, 7, 8},
{9, 10, 11, 12} };
Typically used with nested for loops
Can pass to functions—must specify # columns
e.g. void f2(int arr[ ][4], int nRows);
Col. 0
Col. 1
Col. 2
Col. 3
Row 0
x[0][0]
x[0][1]
x[0][2]
x[0][3]
Row 1
x[1][0]
x[1][1]
x[1][2]
x[1][3]
Row 2
x[2][0]
x[2][1]
x[2][2]
x[2][3]
6/17/2019
ECE Application Programming: Lecture 10

23. ECE Application Programming: Lecture 10
Review: strings
Represented as character arrays
Can be initialized using string constants
char hello[] = “Hello”;
Can access individual elements
hello[3] = ‘l’;
Can print directly or with formatting
Print directly: printf(hello);
Print w/formatting using %s: printf(“%s\n”, hello);
Reading strings: scanf(“%s”, str);
Reads all characters up to (but not including) first space, tab, or newline
Must leave enough room for terminating ‘\0’
6/17/2019
ECE Application Programming: Lecture 10

24. 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
strncpy() not guaranteed to add null terminator
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, 1 if s1 > s2, -1 if s1 < s2
6/17/2019
ECE Application Programming: Lecture 10

25. 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
strncat() guaranteed to add null terminator
6/17/2019
ECE Application Programming: Lecture 10

26. ECE Application Programming: Lecture 10
Final notes
Next time
Exam 2—please be on time
Reminders:
Ch. 7 activities due Thursday
Program 5 to be posted; due Wednesday 6/20
Old spec and starter files (which will become template files) on course schedule page
Exam 2: Monday, 6/18
Will be allowed one 8.5” x 11” note sheet
Covers material from Lec. 6-9 (not structures)
6/17/2019
ECE Application Programming: Lecture 10