\documentclass{beamer}
%include lhs2TeX.fmt
\author{Piyush P Kurur\\
  Office no: 224\\
  Dept. of Comp. Sci. and Engg.\\
  IIT Kanpur}


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\usepackage{tikz}
\usetikzlibrary{positioning,shapes,chains,fit}
\usetikzlibrary{shapes.symbols}
\usetikzlibrary{matrix}
\usetikzlibrary{backgrounds}
\usetikzlibrary{shapes.geometric}
\usepackage{multicol}

\usepackage{algorithm2e}
\usepackage{pgfkeys}
\usepackage{multicol}
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        shape=rectangle,%
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\title{Fundamentals of Computing: Lecture 14}
\date{August 31, 2009}
\begin{document}
\begin{frame}
  \maketitle
\end{frame}

\begin{frame}
  \frametitle{Pointers}
  
  
  \begin{itemize}
    \pause
  \item A pointer is an abstraction of memory address.
    \pause

  \item Value of a pointer variable of type |T| is an address of a
    memory cell capable of storing a value of type |T|.
  \end{itemize}
  
  \pause
  \begin{tikzpicture}
    \node [style=box] at (0,1) (p) 
          [label=above:$\mathtt{ptr}$]{$\cdot$};

    \node [style=box] at (3,0) (x)
          [label=above:$\mathtt{x}$]{$5$};

    \draw [->] (p.mid) to [out=0, in=180] (x.west);
  \end{tikzpicture}

  \pause
  Before we start:

  \begin{block}{WARNING}
    Too much of pointer gymnastics can cause serious injury to
    readability.
  \end{block}
  
\end{frame}

\begin{frame}
  \frametitle{Declaration}
  
  Let |T| be a type then we can declare a pointer to
  |T| as |T *ptr|

  \pause
  \begin{block}{Example}
    \begin{code}
      int x, *p, **pp;
    \end{code}

    \pause
    The above code declares 
    \begin{itemize}
    \item |x| is an integer
    \item |p| is a pointer to an integer
    \item |pp| is a pointer to a pointer to an integer.
    \end{itemize}
  \end{block}
  
\end{frame}

\begin{frame}
  \begin{block}{Dereferencing}
    For a pointer variable |ptr|, |*ptr| is the value stored in the
    location pointed by |ptr|.
  \end{block}
  \pause
  \begin{block}{Conversely}
    If |x| is a variable then |&x| is the address of the variable.
  \end{block}
  
  \pause

  \begin{multicols}{2}
    \uncover<2->{
      \begin{code}
        int x, *p, *pp;
      \end{code}
    }
    \uncover<5->{
      \begin{code}
        x =5;
        p = &x;
        pp = &p;
      \end{code}
    }
    \newpage
    
    \begin{tikzpicture}
      \uncover<4->{
        \node [garbage] at (2,3) (g){$\bot$};
        \node [style=box] at (0,1) (pp) [label=above:$\mathtt{pp}$] {$\cdot$};
        \node [style=box] at (2,0) (p)
              [label=above:$\mathtt{p}$]{$\cdot$};
      }
      \uncover<4-5>{
        \node[style=box]  at (4,1) (x)[label=above:$\mathtt{x}$]{$\bot$};
        \draw [->] (p.mid) to [out=0, in=270] (g.south);
        \draw [->] (pp.mid) to [out=0, in=180] (g.west);
      }
      \uncover<6->{
        \node[style=box]  at (4,1) (x) [label=above:$\mathtt{x}$]{$5$};
        \draw [->] (p.mid) to [out=0, in=180] (x.west);
        \draw [->] (pp.mid) to [out=0, in=180] (p.west);
      }
    \end{tikzpicture}
  \end{multicols}
  
\end{frame}

\begin{frame}
  \frametitle{Swapping: Pointer version}

  \begin{code}
    void swap(int *, int *);
    int main()
    {
      int x=15,y=42;
      printf("x = %d, y = %d\n",x,y);
      swap(&x,&y);
      printf("x = %d, y = %d\n",x,y);
    }
   void swap(int *a, int *b)
   {
     int temp;
     temp = *a;
     *a = *b;
     *b = temp;
   }
  \end{code}
      
\end{frame}

\begin{frame}
  \frametitle{Swapping Pointer version}
  \begin{tikzpicture}
    [background rectangle/.style={draw=yellow!50,fill=yellow!10,rounded corners}]
    %\pgfdeclarelayer{background}
    %\pgfsetlayers{background,main}
    \node [style=box] at (0,1) (x) [label=above:$\mathtt{x}$] {$15$};
    \node [style=box] at (0,-1) (y) [label=above:$\mathtt{y}$] {$42$};
    
    \pause
    \node[style=box] at (3,2) (a)[label=above:$\mathtt{a}$] {$\cdot$};
    \node[style=box] at (3,0) (t)[label=above:$\mathtt{temp}$]{$\bot$};
    \node[style=box] at (3,-2) (b)[label=above:$\mathtt{b}$] {$\cdot$};
    \draw [->] (a.mid) to [out=180, in=0] (x.east);
    \draw [->] (b.mid) to [out=180, in=0] (y.east);
    
    \pause
    \draw [->, line width=0.25em, blue!20] 
        (x.south) to [out=270, in=180] node [black, auto] 
        {$\texttt{temp = *a}$} (t.west);

    \pause
    \node[style=box] at (3,0) (t)[label=above:$\mathtt{temp}$]{$15$};
    
    \pause
    \draw [->, line width=0.25em, blue!20] 
          (y.west) to [out=270, in=180] node [black, auto] 
          {$\texttt{*a = *b}$} (x.west) ;

    \pause
    \node[style=box] at (x) [label=above:$\mathtt{x}$]{$42$};

    \pause
    \draw [->, line width=0.25em, blue!20] 
    (t.south) to [out=270, in=0] node [black, above] {$\texttt{*b=temp}$}  
    (y.north east);
    \pause
    \node[style=box] at (y) [label=above:$\mathtt{y}$]{$15$};



  \end{tikzpicture}
\end{frame}

\end{document}