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POAdding the ! operator and sqrt(), pow() etc. to a calculator example application
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  1. POAdding the ! operator and sqrt(), pow() etc. to a calculator example application
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    copied!<p>I'm doing the exercises in Stroustrup's new book <a href="http://www.stroustrup.com/Programming/" rel="noreferrer">"Programming Principles and Practice Using C++"</a> and was wondering if anyone on SO has done them and is willing to share the knowledge? Specifically about the calculator that's developed in Chap 6 and 7. Eg the questions about adding the ! operator and sqrt(), pow() etc. I have done these but I don't know if the solution I have is the "good" way of doing things, and there are no published solutions on Bjarne's website. I'd like to know if I am going down the right track. Maybe we can make a wiki for the exercises?</p> <p>Basically I have a token parser. It reads a char at a time from cin. It's meant to tokenise expressions like 5*3+1 and it works great for that. One of the exercises is to add a sqrt() function. So I modified the tokenising code to detect "sqrt(" and then return a Token object representing sqrt. In this case I use the char 's'. Is this how others would do it? What if I need to implement sin()? The case statement would get messy. </p> <pre><code>char ch; cin &gt;&gt; ch; // note that &gt;&gt; skips whitespace (space, newline, tab, etc.) switch (ch) { case ';': // for "print" case 'q': // for "quit" case '(': case ')': case '+': case '-': case '*': case '/': case '!': return Token(ch); // let each character represent itself case '.': case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9': { cin.putback(ch); // put digit back into the input stream double val; cin &gt;&gt; val; // read a floating-point number return Token('8',val); // let '8' represent "a number" } case 's': { char q, r, t, br; cin &gt;&gt; q &gt;&gt; r &gt;&gt; t &gt;&gt; br; if (q == 'q' &amp;&amp; r == 'r' &amp;&amp; t == 't' &amp;&amp; br == '(') { cin.putback('('); // put back the bracket return Token('s'); // let 's' represent sqrt } } default: error("Bad token"); } </code></pre>
 

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