1. EECE.3220 Data Structures Instructor: Dr. Michael Geiger Spring 2019
Lecture 5:
Output manipulators
Other input functions

2. Announcements/reminders
Program 1 due Friday, 2/8
All programs to be submitted via Blackboard
Submit a single .zip file containing all files for this assignment
Additional instructor support for course
Grader: Shubham Tikare
Office hours: Tues 9-11 AM, Ball 301E (ECE Conf Rm)
Tutor: Felipe Loera
Hours available on CLASS site (link also on home page)
6/1/2019
Data Structures: Lecture 5

3. Data Structures: Lecture 5
Lecture outline
Program 1 basics
Review
Functions in C++
Output manipulators
Other input methods
Reading space character(s)
Ignoring single character
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Data Structures: Lecture 5

4. Data Structures: Lecture 5
Program 1 basics
Refresher on structures
Gain familiarity with basic C++ I/O
Will use two structures
Point: simple point in 2D plane
Polygon: collection of Point structures +
Number of points
Bounding box (min/max X & Y values) (optional)
Will write functions to
Read contents of Point
Add Points to a Polygon
Display Point and Polygon structures
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Data Structures: Lecture 5

5. Data Structures: Lecture 5
Review: Functions
All examples below are function prototypes
Contain information about how to call function
Return type, name, and argument list
Only arg types required, but good practice to list names
No details on operation of function (definition)
int f1();
double f2(int x, int y);
void f3(int *p1, int *p2);
void f4(int &r1, int &r2);
f3() arguments passed by address
Explicit pointer—call requires addresses: f3(&x, &y);
f4()arguments passed by reference
Aliases—call does not require addresses: f4(x, y);
f4() does have ability to modify input arguments
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Data Structures: Lecture 5

6. Review: Function example
#include <iostream> using namespace std; double f1(int v1, int v2); void f2(int *ptr1, int *ptr2); void f3(int &ref1, int &ref2); int main() { int foo = 10; int bar = 57; double baz; baz = f1(foo, bar); cout << "After f1(), foo = " << foo << ", bar = " << bar << ", baz = " << baz << "\n"; f2(&foo, &bar); cout << "After f2(), foo = " << foo << ", bar = " << bar << "\n"; f3(foo, bar); cout << "After f3(), foo = " << foo return 0; }
double f1(int v1, int v2) { return (v1 + v2) / 2.0; } void f2(int *ptr1, int *ptr2) { while (*ptr1 > 5) { *ptr2 -= 3; (*ptr1)--; void f3(int &ref1, int &ref2) { if (ref1 == 5 && ref2 >= 45) { ref1++; ref2--; else if (ref1 == 5) { ref1--; ref2++; else { ref1 = ref2 - 10; ref2 = ref1 + 10;
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Data Structures: Lecture 5

7. Data Structures: Lecture 5
Example output
After f1(), foo = 10, bar = 57, baz = 33.5 After f2(), foo = 5, bar = 42 After f3(), foo = 4, bar = 43
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Data Structures: Lecture 5

8. Data Structures: Lecture 5
Formatted output
Recall earlier example:
int i, j;
double x, y;
...
cin >> x >> y >> i >> j; // Assume input
cout << "Second output" << endl;
cout << i << ',' << j << ',' << x
<< ',' << y << endl;
x and y are of type double …
... but second cout prints 2 & 3 for x & y
What if we want to
Always print decimal point?
Always show certain number of places after point?
Use stream manipulators: objects affecting output stream
Already seen one of these: endl
To use others, must add #include <iomanip>
May also use stream functions: functions associated with cin/cout
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Data Structures: Lecture 5

9. FP Precision (setprecision)
Precision of floating-point numbers
Number of digits displayed to the right of the decimal point
setprecision parameterized stream manipulator
Precision settings are sticky
Do not change until you’ve explicitly changed them
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Data Structures: Lecture 5

10. Example: setprecision
#include <iostream> using std::cout; using std::endl; using std::fixed; #include <iomanip> using std::setprecision; #include <cmath> using std::sqrt; // sqrt prototype
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Data Structures: Lecture 5

11. Example: setprecision (cont.)
int main() {
double root2 = sqrt( 2.0 ); // calc square root of 2
int places; // precision, vary from 0-9
cout << "Square root of 2 with precisions 0-9."
<< endl;
cout << fixed; // use fixed point format (not sci. not)
// set precision for each digit, then show square root
for ( places = 0; places <= 9; places++ )
cout << setprecision( places ) << root2 << endl;
return 0;
} // end main
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Data Structures: Lecture 5

12. Data Structures: Lecture 5
Example output
Square root of 2 with precisions
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Data Structures: Lecture 5

13. Trailing Zeros and Decimal Points (showpoint)
Stream manipulator showpoint
Floating-point numbers are output with decimal point and trailing zeros
Example
79.0 prints as instead of 79
Reset showpoint setting with noshowpoint
Implies a default precision of 6
Can override with setprecision
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Data Structures: Lecture 5

14. Example: showpoint, setprecision
#include <iostream> #include <iomanip> using namespace std; int main() { double i, j, x, y; cin >> i >> j >> x >> y; // Input: cout << fixed << showpoint; cout << "First output " << endl; cout << i << ',' << j << ',' << setprecision(3) << x << ',' << y << endl; return 0; } OUTPUT: First output , ,3.400,5.000
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Data Structures: Lecture 5

15. Data Structures: Lecture 5
Characters and input
>> discards leading whitespace
get() method used to input whitespace characters
Optional second argument allows you to input multiple characters
Default is 1
cin.get(buffer, 10) reads 10 characters from input
Example:
int x;
char ch;
cin >> x >> ch;
cin >> x;
cin.get(ch); x ch 45 39
‘\n ’
‘c’
Input stream:
45 c 39 b
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Data Structures: Lecture 5

16. Characters and input (cont.)
Reading an entire line: getline(char[], num)
Reads up to num characters on a line
Stops at newline character
Example: cin.getline(buffer, 10);
Must be careful if input is read using stream extraction operator ( >> ) as well as getline()
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Data Structures: Lecture 5

17. Data Structures: Lecture 5
getline example
int numR;
char name[20];
cin >> numR;
cin.getline(name, 20);
If input is: 6
Room 12
what values do numR and name hold?
numR = 6
name = “\n”  why?
cin >> numR stops at any whitespace character  \n
cin.getline(name,20) starts with next char, ends at newline
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Data Structures: Lecture 5

18. Fixing getline example
Skipping whitespace characters: ignore(num)
Discards num characters from input stream without storing them
To fix previous example:
int numR;
char name[20];
cin >> numR;
cin.ignore(1);
cin.getline(name, 20);
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Data Structures: Lecture 5

19. Data Structures: Lecture 5
Final notes
Next time
Finish input functions, C++ strings
Reminders:
Program 1 due Friday, 2/8
All programs to be submitted via Blackboard
Submit a single .zip file containing all files for this assignment
Additional instructor support for course
Grader: Shubham Tikare
Office hours: Tues 9-11 AM, Ball 301E (ECE Conf Rm)
Tutor: Felipe Loera
Hours available on CLASS site (link also on home page)
6/1/2019
Data Structures: Lecture 5