1. EECE.3220 Data Structures Instructor: Dr. Michael Geiger Spring 2019
Lecture 2:
C++ program structure
Basic I/O in C++

2. Data Structures: Lecture 2
Lecture outline
Announcements/reminders
Program 1 due date TBD (within 2 weeks or so … probably less)
Today’s lecture
Basic C++ program structure
I/O in C++
5/22/2019
Data Structures: Lecture 2

3. Data Structures: Lecture 2
Hello World! in C++
#include <iostream> // C++ input/output library using namespace std; int main() { cout << "Hello World!\n"; return 0; }
5/22/2019
Data Structures: Lecture 2

4. Namespaces; using Directive
The using directive instructs the compiler to use files defined within a specific namespace
Namespaces allow us to declare different scopes
Typically written right after the relevant header file(s)
Example: using namespace std;
std is the name of the Standard C++ namespace
Including this line avoids listing namespace for every identifier in headers …
… but allows everything in the std namespace
Compromise: list namespace members actually used
using std::cout;
Otherwise, you’d have to write “std::cout” every time
Which you prefer is matter of style
5/22/2019
Data Structures: Lecture 2

5. Data Structures: Lecture 2
Review: C I/O basics
Output: printf()
Prints most characters exactly as shown in quotes
To print variables, provide format specifiers + comma-separated list of variables
Format specifiers provide type, formatting
We covered precision; also field width & extra characters
Example: printf("x = %.2lf\n", x);
Input: scanf()
Arguments: string with format specifiers, address list
Reading numbers skips whitespace
Reading chars skips whitespace if space before %c
Example: scanf("%d %c%d”, &v1, &c1, &v2);
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Data Structures: Lecture 2

6. C++ I/O basics: I/O streams
C++ has three standard input/output streams
cin is the standard input (e.g., keyboard)
cout is the standard output
cerr is the standard error
5/22/2019
Data Structures: Lecture 2

7. C++ I/O basics: Standard output
Insertion operator << directs data to cout
General Form: cout << expr << expr;
expr can be any C++ constant, identifier, formula, or function call
endl: newline (like'\n'); also flushes buffer
Forces output to be printed immediately
Example: cout << "x = " << x << endl;
No need to specify type for x—simply insert in output
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Data Structures: Lecture 2

8. Modified program: two cout statements
#include <iostream>
using std::cout; // Only include part
// of std namespace
// you actually use
int main() {
// display message
cout << "Welcome ";
cout << "to C++!\n";
return 0; }
5/22/2019
Data Structures: Lecture 2

9. Modified program: multiple output lines
#include <iostream>
using std::cout;
int main() {
cout << "Welcome\nto\n\nC++!\n";
return 0; }
5/22/2019
Data Structures: Lecture 2

10. C++ I/O basics: standard input
Extraction operator >> to direct keyboard input to variables
General Form: cin >> identifier >> identifier;
Input value must be compatible with identifier type
Extraction operator always ignores leading whitespace
5/22/2019
Data Structures: Lecture 2

11. C++ input/output example
#include <iostream> using std::cout; using std::cin; using std::endl; int main() { int number1, number2; // Input variables // prompt user for data and read into appropriate variables cout << "Enter first integer: "; cin >> number1; cout << "Enter second integer: "; cin >> number2; cout << "Sum is " << number1 + number2 << endl; // display sum; end line return 0; }
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Data Structures: Lecture 2

12. Example 1: find output
#include <iostream> using std::cout; using std::cin; using std::endl; int main() { int i, j; double x; cin >> i >> j; cin >> x; cout << "output \n"; cout << i << ',' << j << endl << x << "cm" << endl; return 0; }
Assume following input:
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ECE 264: Lecture 4

13. Example 2: find output
#include <iostream> using std::cout; using std::cin; using std::endl; int main() { int i, j; double x, y; cin >> i >> j >> x >> y; cout << "First output " << endl; cout << i << ',' << j << ',' << x << ',' << y << endl; cin >> x >> y >> i >> j; cout << "Second output" << endl; return 0; }
Assume following input:
1 2
3.4 5
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ECE 264: Lecture 4

14. Data Structures: Lecture 2
Solutions
Example 1 (note lack of spaces):
output
1,2
4.5cm
Example 2:
First output
1,2,3.4,5
Second output
3,?,2,3
In VS, j unchanged  ? = 2
In Xcode, j set to 0  ? = 0
Key point: make sure types match
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Data Structures: Lecture 2

15. Data Structures: Lecture 2
Final notes
Next time: more on going from C to C++
Structures in C++
Reminders:
Sign up for the course discussion group on Piazza!
Program 1 due date TBD (within 2 weeks or so)
All programs to be submitted via Dropbox
Dr. Geiger for access to shared Dropbox folder
5/22/2019
Data Structures: Lecture 2