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    <title>Programming in C and C++ -- 2020/21 -- Supervision 1</title>
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    <h1>Programming in C and C++ (2020/21)<br/>Supervision 1</h1>

    <h2>1</h2>
    <p>What is the difference between <code>'a'</code> and <code>"a"</code>?</p>

    <hr />

    <h2>2</h2>
    <p>Does the following code terminate? And if so, under which conditions?</p>

    <pre>
    char i, j;
    for (i = 0; i &lt; 10, j &lt; 5; i++, j++);
    </pre>

    <hr />

    <h2>3</h2>
    <p>Write an implementation of <strong>bubble sort</strong> for a fixed array of integers. An array of integers can be defined as <code>int i[] = {1, 2, 3, 4};</code></p>

    <p>Use function recursion to write an implementation of merge sort for a fixed array of integers. How much memory does your program use for a list of length <em>n</em>?</p>

    <hr />

    <h2>4</h2>
    <p>Implement a function <code>&nbsp;int cntlower(char str[])&nbsp;</code> that, given a string, returns the number of lower-case letters it contains.</p>

    <hr />

    <h2>5</h2>
    <p>Define a macro <code>SWAP(t, x, y)</code> that swaps two arguments <code>x</code> and <code>y</code> of type <code>t</code>. Does your macro work as expected when called as <code>SWAP(int, v[i++], w[f(x)])</code>?</p>

    <p>What other invocations could cause a simple implementation to fail and how can we mitigate them?</p>

    <hr />

    <h2>6</h2>
    <p>Define a macro <code>SWAP(x, y)</code> that swaps <code>x</code> and <code>y</code> of the same type without using any extra memory.</p>

    <hr />

    <h2>7</h2>
    <p>Given a pointer <code>p</code>, what does the expression <code>p[-2]</code> mean, and when is it legal?</p>

    <hr />

    <h2>8</h2>
    <p>Write a string search function with a declaration of</p>

    <pre>
    char *strfind(const char *s, const char *f);</pre>

    <p>which returns a pointer to the first occurrence of <code>s</code> in <code>f</code> (and <code>NULL</code> otherwise)</p>

    <hr />

    <h2>9</h2>
    <p>Write a program <code>calc</code> which evaluates an expression in Reverse Polish Notation given on the command line; for example</p>

    <pre>
    $ calc 2 3 4 + \*</pre>

    <p>should print 14. The character <code>*</code> needs to be escaped with a backslash in some shells or otherwise it gets expanded to all the files in your current directory.</p>

    <hr />

    <h2>10</h2>
    <p>What is the value of <code>i</code> after executing each of the following:</p>

    <ol>
        <li><code>i = sizeof(char);</code></li>
        <li><code>i = sizeof(int);</code></li>
        <li><code>int a; i = sizeof a;</code></li>
        <li><code>char b[5]; i = sizeof(b);</code></li>
        <li><code>char *c=b; i = sizeof(c);</code></li>
        <li><code>struct { int d; char e;} s; i = sizeof s;</code></li>
        <li><code>void f(int j[5]) { i = sizeof j;}</code></li>
        <li><code>void f(int j[][10]) { i = sizeof j; }</code></li>
    </ol>

    <hr />

    <h2>11</h2>
    <p>A spacecraft arrives on Mars, but its memory has been corrupted by radiation en
    route. Luckily, it can receive updates one bit at a time using a predefined C
    function <code>short receive_bit(void)</code>, that when called will return either 1 or 0.
    The stream of bits for a value is transmitted in unsigned big-endian byte order:
    for example, a 16-bit value of 125 would be 0000000001111101. Assume the <code>int</code>
    type is 32 bits.</p>

    <ol>
        <li><p>Explain the meaning of the <code>inline</code> keyword on C function declarations, and a
        potential drawback of using it.</p></li>

        <li><p>Using <code>receive_bit()</code>, define a function <code>receive_int()</code> that decodes and
        returns a 32-bit value from the sequence of received bits.</p></li>

        <li><p>(<em>optional</em>) Build a more general decoding function receive using a C++
        template with two parameters that specify the number of bits to decode and a
        datatype for the decoded value. Use this to write two template instantiations
        that decode an 8-bit value into a short and a 32-bit value into an unsigned
        long.</p></li>

        <li><p>Find and explain <em>four</em> instances of undefined behaviour that could result
        from compiling and running the C code below with different command-line
        arguments.
        The <code>strcpy(dst,src)</code> function copies a zero-terminated C string from the
        <code>src</code> buffer to the <code>dst</code> buffer. The <code>putchar(c)</code> function outputs a
        character c to the console. You can assume that the standard C header
        prototypes have been included for <code>&lt;stdio.h&gt;</code>, <code>&lt;stdlib.h&gt;</code> and <code>&lt;string.h&gt;</code>.</p>

        <pre>
    char *show_instruction(int msg) {
        char buf[6];
        int fuel;
        if (msg == 1 &amp;&amp; fuel--) {
            strcpy(buf, "THRUST");
            return buf;
        } else if (msg == 2) {
            char *msg = (char *)malloc(100);
            strcpy(msg, "DEPLOY_PARACHUTE");
            return msg;
        }
    }

    int main(int argc, char **argv) {
        char *msg;
        msg = show_instruction(argc);
        putchar(msg[0]);
        return 0;
    }
        </pre></li>
    </ol>

    <p>&nbsp;</p>
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