1. 16.216 ECE Application Programming
Instructor: Dr. Michael Geiger
Summer 2012
Lecture 11
Structures
Exam 3 Preview

2. ECE Application Programming: Lecture 11
Lecture outline
Announcements/reminders
Program 8 due Friday, 8/17 at noon
Starter file now available
Exam 3 Thursday, 8/16
Today’s lecture:
Structures
Exam 3 Preview
7/22/2018
ECE Application Programming: Lecture 11

3. ECE Application Programming: Lecture 11
Review: File I/O
Open file: FILE *fopen(filename, file_access)
Close file: fclose(file_handle)
Formatted I/O:
fprintf(file_handle, format_specifier, 0+ variables)
fscanf(file_handle, format_specifier, 0+ variables)
Unformatted I/O:
size_t fwrite(pointer, element size, # elements, file_handle)
size_t fread(pointer, element size, # elements, file_handle)
Check for EOF using either fscanf() result or feof(FILE *)
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ECE Application Programming: Lecture 11

4. Review: Unformatted I/O (cont.)
Character I/O
int fputc(int c, FILE *stream);
int putchar(int c);
int fgetc(FILE *stream);
int getchar();
int ungetc(int c, FILE *stream);
Line I/O
int fputs(const char *s, FILE *stream);
int puts(const char *s);
char *fgets(char *s, int n, FILE *stream);
char *gets(char *s);
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ECE Application Programming: Lecture 11

5. ECE Application Programming: Lecture 11
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
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ECE Application Programming: Lecture 11

6. 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 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 11

7. ECE Application Programming: Lecture 11
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 11

8. 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 11

9. 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 11

10. ECE Application Programming: Lecture 11
Example solution
A = i B = i C = i D = i E = i
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ECE Application Programming: Lecture 11

11. Structure assignments, pointers
As seen previously: once structure defined, can assign variables of that type to one another
Will work both for scalars and arrays
Can also have pointers to structures
Special notation to access structure elements through pointer: <ptr>-><element name>
Example:
StudentInfo *p = &student1;
p->GPA = 3.5;
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ECE Application Programming: Lecture 11

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);
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ECE Application Programming: Lecture 11

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 11

14. ECE Application Programming: Lecture 11
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 11

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; }
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ECE Application Programming: Lecture 11

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 11

17. ECE Application Programming: Lecture 11
Exam 3 notes
Allowed one 8.5” x 11” two-sided note sheet
No other notes or electronic devices
Exam lasts 3 hours (but is written for ~50 min)
Covers all lectures after Exam 2
Format similar to Exams 1/2
1 multiple choice problem (File I/O, unformatted I/O, & structures)
1 code reading problem
1 code writing problem
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ECE Application Programming: Lecture 11

18. Review: arrays & pointer arithmetic
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
Can use pointer to access array
Can use arithmetic to move pointer through array
p + 1  points to next element (after where p currently points)
p++  move pointer and point to next element
p--  move pointer and point to previous element
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ECE Application Programming: Lecture 11

19. ECE Application Programming: Lecture 11
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
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]
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ECE Application Programming: Lecture 11

20. ECE Application Programming: Lecture 11
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);
Must leave enough room for terminating ‘\0’
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ECE Application Programming: Lecture 11

21. 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
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
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ECE Application Programming: Lecture 11

22. 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 11

23. ECE Application Programming: Lecture 11
Review: File I/O
Open file: FILE *fopen(filename, file_access)
Close file: fclose(file_handle)
Formatted I/O:
fprintf(file_handle, format_specifier, 0+ variables)
fscanf(file_handle, format_specifier, 0+ variables)
Unformatted I/O:
size_t fwrite(pointer, element size, # elements, file_handle)
size_t fread(pointer, element size, # elements, file_handle)
Check for EOF using either fscanf() result or feof(FILE *)
7/22/2018
ECE Application Programming: Lecture 11

24. Review: Unformatted I/O (cont.)
Character I/O
int fputc(int c, FILE *stream);
int putchar(int c);
int fgetc(FILE *stream);
int getchar();
int ungetc(int c, FILE *stream);
Line I/O
int fputs(const char *s, FILE *stream);
int puts(const char *s);
char *fgets(char *s, int n, FILE *stream);
char *gets(char *s);
7/22/2018
ECE Application Programming: Lecture 11

25. ECE Application Programming: Lecture 11
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;
Access members using
Dot operator: student1.middle = ‘J’;
Arrow (if pointers): sPtr->GPA = 3.5;
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ECE Application Programming: Lecture 11

26. ECE Application Programming: Lecture 11
Next time
Exam 3
7/22/2018
ECE Application Programming: Lecture 11