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

ECE Application Programming: Lecture 10 Lecture outline Announcements/reminders Program 6 due tomorrow Program 7 due Wednesday, 6/14 Exam 2: Monday, 6/12 Will be allowed one 8.5” x 11” note sheet Today’s lecture Structures Exam 2 Preview 4/7/2019 ECE Application Programming: Lecture 10

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' 4/7/2019 ECE Application Programming: Lecture 10

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 4/7/2019 ECE Application Programming: Lecture 10

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 4/7/2019 ECE Application Programming: Lecture 10

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 4/7/2019 ECE Application Programming: Lecture 10

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 4/7/2019 ECE Application Programming: Lecture 10

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; 4/7/2019 ECE Application Programming: Lecture 10

Using structure variables Initialization very similar to array initialization: StudentInfo student1 = { “John”, ‘Q’, “Smith”, 12345678, 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; 4/7/2019 ECE Application Programming: Lecture 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; } 4/7/2019 ECE Application Programming: Lecture 10

ECE Application Programming: Lecture 10 Example solution A = 1.00 + 2.00i B = 3.40 + 5.60i C = 1.00 + 2.00i D = 4.40 + 7.60i E = -2.40 + -3.60i Note: code in handout has spaces before and after ‘+’ for readability; code on previous slide doesn’t because it wouldn’t fit! 4/7/2019 ECE Application Programming: Lecture 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); 4/7/2019 ECE Application Programming: Lecture 10

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 #12345678 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 #: 12345678 Enter GPA: 1.23 4/7/2019 ECE Application Programming: Lecture 10

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); } 4/7/2019 ECE Application Programming: Lecture 10

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; } 4/7/2019 ECE Application Programming: Lecture 10

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; } 4/7/2019 ECE Application Programming: Lecture 10

ECE Application Programming: Lecture 10 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; 4/7/2019 ECE Application Programming: Lecture 10

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 4/7/2019 ECE Application Programming: Lecture 10

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 1 multiple choice (character arrays and strings) 1 code reading (arrays) 1 code writing (complete 2 of 3 parts; all 3 for extra credit) (functions) 4/7/2019 ECE Application Programming: Lecture 10

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 4/7/2019 ECE Application Programming: Lecture 10

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 4/7/2019 ECE Application Programming: Lecture 10

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, -3.233}; 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); 4/7/2019 ECE Application Programming: Lecture 10

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] 4/7/2019 ECE Application Programming: Lecture 10

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’ 4/7/2019 ECE Application Programming: Lecture 10

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 4/7/2019 ECE Application Programming: Lecture 10

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 4/7/2019 ECE Application Programming: Lecture 10

ECE Application Programming: Lecture 10 Final notes Next time Exam 2 Reminders: Program 6 due tomorrow Program 7 due Wednesday, 6/14 Exam 2: Monday, 6/12 Will be allowed one 8.5” x 11” note sheet 4/7/2019 ECE Application Programming: Lecture 10