1. EECE.3220 Data Structures Instructor: Dr. Michael Geiger Spring 2019
Lecture 3:
Structures in C++

2. Announcements/reminders
Program 1 due date TBD (within 2 weeks or so)
All programs to be submitted via Blackboard
Good C++ reference site:
Basic tutorials + in-depth reference pages
Relevant tutorials under “Reading” on schedule page
Shubham Tikare assigned as grader for course
Will announce his office hours ASAP
Poll to be posted to schedule Exam 1 & 2
Final exam time set: Wednesday, 5/8, 3-6 PM
6/6/2019
Data Structures: Lecture 3

3. Data Structures: Lecture 3
Lecture outline
Review
Basic C++ program structure
I/O in C++
Structs in C++
Working with multiple files
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Data Structures: Lecture 3

4. Review: basic program structure
Covered basic C++ program structure—very similar to C!
#include directive: add libraries to program
<iostream>: basic input/output
Namespaces
Introduced std namespace—includes cin, cout, etc.
Could include entire namespace:
using namespace std;
Or, just include members being used:
using std::cout;
Using statements directly after relevant #include
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Data Structures: Lecture 3

5. Review: Hello World! in C++
#include <iostream> // C++ input/output library using namespace std; int main() { cout << "Hello World!\n"; return 0; }
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Data Structures: Lecture 3

6. Data Structures: Lecture 3
Review: Basic I/O
Output (cout) streams
Can output multiple values in same statement
cout << "x= " << x << ", y=" << y << endl;
Recall endl ≈ ’\n’ + flush output stream
Input (cin) streams
Use cin to read values into variables
E.g., cin >> x;
Skips whitespace characters
Can cause problems if input doesn’t match variable type
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Data Structures: Lecture 3

7. Data Structures: Lecture 3
Review: File I/O
File stream objects
Must include <fstream>
ifstream (input) or ofstream (output)
Have methods for file open/close
File I/O syntax similar to standard I/O
Replace cin/cout with appropriate stream object
Same operators used: << >>
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Data Structures: Lecture 3

8. Data Structures: Lecture 3
File I/O example
#include <fstream> #include <iostream> using std::ifstream; using std::ofstream; int main() { int x, y; ifstream infile; ofstream outfile; // Open input, output files infile.open("f1.txt"); outfile.open("f2.txt"); // Read integer values, then reprint to output infile >> x >> y; outfile << "x = " << x << ", y = " << y << endl; return 0; }
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Data Structures: Lecture 3

9. Review: Structures in C
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;
Typically passed to functions by address
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Data Structures: Lecture 3

10. Data Structures: Lecture 3
Structures in C++
99% the same as in C
Only (visible) difference: typedef isn’t necessary
Could rewrite previous structure definition as:
struct StudentInfo {
char first[50];
char middle;
char last[50];
unsigned int ID;
double GPA; };
Declarations shown in previous slide still work
You can use StudentInfo as type name
In C, type would be struct StudentInfo
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Data Structures: Lecture 3

11. Data Structures: Lecture 3
Structure example
#include <iostream> using namespace std; struct Point { double x; double y; }; int main() { Point p1 = {3, 5}; Point p2 = {7.8, 9.1}; cout << "p1: (" << p1.x << ", " << p1.y << ")\n"; cout << "p2: (" << p2.x << ", " << p2.y << ")\n";
// Assume user enters -1 1 cout << "Enter new x, y for p1: "; cin >> p1.x >> p1.y; p2 = p1; p2.x -= 1.2; p1.y *= 2; cout << "p1: (" << p1.x << ", " << p1.y << ")\n"; cout << "p2: (" << p2.x << ", " << p2.y << ")\n"; return 0; }
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Data Structures: Lecture 3

12. Example solution (user input underlined)
Enter new x, y for p1: -1 1
p1: (-1, 2)
p2: (-2.2, 1)
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Data Structures: Lecture 3

13. Data Structures: Lecture 3
Nested structures
Structures can contain other structures:
struct Name {
char first[50]; // First name
char middle; // Middle initial
char last[50]; // Last name };
struct SINew {
Name sname; // Student name
unsigned int ID; // ID #
double GPA; // Grade point
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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Data Structures: Lecture 3

14. Typical file usage with structures
Each structure has its own .h/.cpp files
.h file (i.e., Name.h, SINew.h) contains structure definition and prototypes of related functions
.cpp file (i.e., Name.cpp, SINew.cpp) contains function definitions
To use struct type and functions, include .h file
SINew.h would include Name.h
Allows Name variable inside SINew structures
Main program could include both …
… although that’s redundant—including SINew.h implicitly includes Name.h
Will organize classes similarly
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Data Structures: Lecture 3

15. Avoiding multiple inclusion of .h files
Say we have two files that start as shown:
file1.h:
#include "file2.h"
...
myprogram.cpp:
#include "file1.h"
What’s the problem?
What does an #include directive really do?
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Data Structures: Lecture 3

16. Avoiding multiple inclusion of .h files
Anything in file2.h is included twice
#include directive copies/pastes contents of file
Compiler will think program redefines structures, function prototypes, etc.
Solution: conditional compilation
Header files include header guard code to ensure they’re only compiled once
Example code for fictional file2.h:
#ifndef file2_h // Start of file
#define file2_h
...
#endif // End of file
Code between #ifndef & #endif only compiled once
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Data Structures: Lecture 3

17. Data Structures: Lecture 3
Final notes
Next time: more on going from C to C++
Functions
Argument passing in C++
(Maybe) I/O manipulators for output formatting
Discussion of Program 1 requirements
Reminders:
Program 1 due date TBD (within 2 weeks or so)
All programs to be submitted via Blackboard
6/6/2019
Data Structures: Lecture 3