Informatik 1Woche 9Moritz Schneider

Moritz Schneider 2. Mai 2019 1

Outline

1. Streams

2. Function Overloading

3. Classes

4. Repetition: Recursion

Moritz Schneider 2. Mai 2019 2

Streams

• Streams werden benoetigt um Werte einzulesen oder auszugeben

• Beispiel: std :: cout oder std :: cin

• peek () oberster Charakter nur ansehen nicht einlesen

• >> : oberstere Charakter einlesen• CodeExpert Beispiel:

– char lookahead (std :: istream & is)– bool consume (std :: istream & is , char expected )

Moritz Schneider 2. Mai 2019 3

Function Overloading

int fun1 (int a) { ... }int fun1 (int a, int b) { ... }

→ Für Compiler eindeutig unterscheidbar→ gültiges (C) C++

int fun2 (int a) { ... }int fun2 ( float a) { ... }

→ Typ wichtig (int ↔ float )→ Parametername (a) egal

Moritz Schneider 2. Mai 2019 4

Function Overloading II

int fun3 (int a) { ... }int fun3 (int b) { ... } // compiler error

→ Für Compiler nicht unterscheidbar→ Parametername ist kein Entscheidungskriterium, da oft nicht mitgegeben.

int c = func (3); // unklar (kein Parametername )

int fun4 (int a) { ... }double fun4 (int a) { ... } // compiler error

→ Nicht unterscheidbardouble d = func4 (3); // unklar ( impliziter cast moeglich )

Moritz Schneider 2. Mai 2019 5

Function Overloading III

#include <iostream >void out (const int i) {

std::cout << i << "␣(int)\n";}void out (const double i) {

std::cout << i << "␣(double )\n";}int main () {

out (3.5); // 3.5 (double)out (2); // 2 (int)out (2.0); // 2 (double)out (0); // 0 (int)out (0.0); // 0 (double)return 0;

}Moritz Schneider 2. Mai 2019 6

Classes

• Ähnlich wie struct

• Aber: private Methoden/Member

class rect {private:

int x1 , y1 , x2 , y2; // private memberpublic:

int flaeche () { // public memberfunktionint fl = (x1 -x2) * (y2 -y1);if (fl < 0) return -fl;else return fl;

};}

Moritz Schneider 2. Mai 2019 7

Classes II - Deklaration vs Definition

Deklaration: rect.h

class rect {private:

int x1 , y1 , x2 , y2;public:

int flaeche ();

// Definition geht auchint get_x1 () { return x1; }

}

Definition: rect.cpp

#include "rect.h"

// POST: return area of the rectint rect:: flaeche () {

int fl = (x1 -x2) * (y2 -y1);if (fl < 0) return -fl;else return fl;

}

Moritz Schneider 2. Mai 2019 8

Classes III - KonstruktorenKonstruktoren werden zum initialisieren benoetigt:

class rect {private:

int x1 , x2 , y1 , y2 , fl;public:

rect(int p1_x , int p1_y , int p2_x , int p2_y) :x1(p1_x), x2(p2_x), y1(p1_y), y2(p2_y) {

fl = flaeche ();}~rect() {

// loeschen von variablen// int , float , vector etc automatisch geloescht// pointer: muss selbst geloescht werden!

}}

Moritz Schneider 2. Mai 2019 9

Beispiel: Operator Überladen

Addition von zwei Punkten:class point {

private :int x, y;

public :point (x_inp , y_inp ): x( x_inp ), y( y_inp ) {};

};

point operator +( const point &first , const point & second ) {return point ( first .x + second .x, first .y + second .y);

}

Oder:point point :: operator +( const point & second ) {

return point (this ->x + second .x, this ->y + second .y);}

Moritz Schneider 2. Mai 2019 10

TriBool

CodeExpert

Moritz Schneider 2. Mai 2019 11

Recursion Exercise 1

Recursion Exercise 1

Rewrite the following recursive function in iterative form.

(From: Script Exercise 128) 2

unsigned int f (const unsigned int n)

{

if (n <= 2) return 1;

return f(n-1) + 2 * f(n-3);

}

Recursion Exercise 1

(From: Script Exercise 128) 3

unsigned int f_it (const unsigned int n)

{

if (n <= 2) return 1;

unsigned int a = 1; // f(0)

unsigned int b = 1; // f(1)

unsigned int c = 1; // f(2)

for (unsigned int i = 3; i < n; ++i) {

const unsigned int a_prev = a; // f(i-3)

a = b; // f(i-2)

b = c; // f(i-1)

c = b + 2 * a_prev; // f(i)

}

return c + 2 * a; // f(n-1) + 2 * f(n-3)

}

Solution below uses just 4 variables.Other solutions are of course also possible.

Recursion Exercise 2

Recursion Exercise 2

Rewrite the following recursive function in iterative form.

(From: Script Exercise 129) 5

unsigned int f (const unsigned int n)

{

if (n == 0) return 1;

return f(n-1) + 2 * f(n/2);

}

Recursion Exercise 2

(From: Script Exercise 129) 6

unsigned int f_it (const unsigned int n)

{

if (n == 0) return 1; // special case

std::vector<unsigned int> f_values(n+1, 0);

f_values[0] = 1;

for (unsigned int i=1; i<=n; ++i)

f_values[i] = f_values[i-1] + 2*f_values[i/2];

return f_values[n];

}

Solution below stores intermediate results in a vector.Other solutions are of course also possible.

Recursion Exercise 3

Recursion Exercise 3

Write a function rev_out (see template below) which outputs the contents of an istream in reverse order using recursion.

8

#include <iostream>

#include <sstream>

// POST: output the content of is in reverse order to

// std::cout, and removed it from is.

void rev_out (std::istream& is)

{

// your code

}

int main () {

std::stringstream input ("abcdefghijklmno");

rev_out (input);

return 0;

}

Recursion Exercise 3

9

Other solutions are of course also possible.

#include <iostream>

#include <sstream>

// POST: output the content of is in reverse order to

// std::cout, and removed it from is.

void rev_out (std::istream& is)

{

char val;

if (is >> val) {

rev_out(is);

std::cout << val;

}

}

int main () {

std::stringstream input ("abcdefghijklmno");

rev_out (input);

return 0;

}

Fragen?

Moritz Schneider 2. Mai 2019 12