teaching machines

CS 330 Lecture 20 – C++

March 10, 2014 by Chris Johnson. Filed under cs330, lectures, spring 2014.

Agenda

• what ?s
• Bjarne’s philosophy
• C with Classes
• C++ inheritance
• a Function hierarchy
• one language?

Think About This

class A {
  A tweakTweak(int a) {
    return new A();
  }
}

class B extends A {
  @Override
  B tweakTweak(int a) {
    return new B();
  }
}

class A {
  A tweakTweak(int a) {
    return new A();
  }
}

class C extends A {
  @Override
  A tweakTweak(double a) {
    return new A();
  }
}

C with Classes

class PegasusBoots {
  public:
    PegasusBoots(int strength) {
      this->strength = strength;
    }

    int getStrength() const {
      return strength;
    }

    void engage(Hero h) {
      h.setJumpFactor(getStrength());
    }

    static const std::string& getPartNumber() {
      return "#JF1273";
    }
  private:
    int strength;
}

Polymorphism without Conditions

• http://www.antiifcampaign.com
• http://www.refactoring.com/catalog/replaceConditionalWithPolymorphism.html

Code

Function.h

#ifndef FUNCTION_H
#define FUNCTION_H

class Function {
  public:
    virtual double EvaluateAt(double x) const = 0;
};

#endif

SineFunction.h

#ifndef SINEFUNCTION_H
#define SINEFUNCTION_H

#include "Function.h"

class SineFunction : public Function {
  public:
    double EvaluateAt(double x) const;
};

#endif

SineFunction.cpp

#include <iostream>
#include <cmath>

#include "SineFunction.h"

/* ------------------------------------------------------------------------- */

double SineFunction::EvaluateAt(double x) const {
  return sin(x); 
}

/* ------------------------------------------------------------------------- */

graph_drawer.cpp

#include <iostream>
#include "Function.h"
#include "SineFunction.h"

/* ------------------------------------------------------------------------- */

void draw(const Function &f);

/* ------------------------------------------------------------------------- */

int main(int argc, char **argv) {
  SineFunction sine;
  draw(sine);
  return 0;
}

/* ------------------------------------------------------------------------- */

void draw(const Function &f) {
  const int NROWS = 21;
  const int NCOLS = 51;

  char plot[NROWS][NCOLS];

  for (int r = 0; r < NROWS; ++r) {
    for (int c = 0; c < NCOLS; ++c) {
      plot[r][c] = ' ';
    }
  }

  for (int c = 0; c < NCOLS; ++c) {
    plot[NROWS / 2][c] = '-';
  }

  for (int r = 0; r < NROWS; ++r) {
    plot[r][NCOLS / 2] = '|';
  }

  plot[NROWS / 2][NCOLS / 2] = '+';

  for (int c = 0; c < NCOLS; ++c) {
    double x = c / (NCOLS - 1.0) * 6.0 - 3.0;
    double y = f.EvaluateAt(x);
    int r = (int) (y * NROWS * 0.5 + NROWS * 0.5);
    if (r >= 0 && r < NROWS) {
      plot[r][c] = '.';
    }
  }

  for (int r = NROWS - 1; r >= 0; --r) {
    for (int c = 0; c < NCOLS; ++c) {
      std::cout << plot[r][c];
    }
    std::cout << std::endl;
  }
}

/* ------------------------------------------------------------------------- */

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