Mark: 5 revision(s)

2008-11-03T05:20:27Z

5 revision(s)

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To get start with the lab I tried to compile the file and it gave me an error. I changed:
<pre>
return sp >= str && stircmp( sp, end ) == 0
</pre>
<pre>
return sp >= str && stricmp( sp, end ) == 0
</pre>
it can compile now
.Then i construct an expression using mkNode that, when passed to
prefix tree, produces the output -(-(a b)).
<pre>
ParseTree* t = mkNode( ’-’, mkNode( ’-’, mkNode( ’a’, 0 ), mkNode( ’b’, 0 ), 0 ),0).;
</pre>
in order to make sure it is right i wrote a main function.
i aslo got a graph for the tree.
<sorry i can't upload it>

.After that i construct an expression that producesn ?(>(+(a b) c) *(z +(y b)) ?(=(a 2) -(x y) -(y x))).
<pre>
ParseTree* t = mkNode( '?',mkNode( '>', mkNode('+',mkNode( 'a', 0 ), mkNode( 'b', 0 ),0),mkNode('c',0),0) ,mkNode('*',mkNode( 'z',mkNode( '+', mkNode( 'y', 0 ), mkNode( 'b', 0 ), 0 ),0),0),mkNode('?',mkNode( '=',mkNode( 'a',0), mkNode( '2', 0 ),0), mkNode( '-', mkNode('x',0 ),mkNode('y', 0 ),0), mkNode( '-', mkNode('y',0 ),mkNode('x', 0 ),0),0),0);
</pre>
i toke me a while to figured out which 0 goes to which.
.I have a graph for that tree but i can't upload it .
.Question mark has three children. The second and third children are the thing goes to the left and right hand side of colon.
.I write a (recursive) function to evaluate a parse tree that consists of nodes that are either digits or the operators +, -, * and /.
<pre>
eval(ParseTree *node){

if (node->name=='+'){
return eval(node->arg[0])+eval(node->arg[1]);
}
if (node->name=='-'){
return eval(node->arg[0])-eval(node->arg[1]);
}
if (node->name=='/'){
return eval(node->arg[0])/eval(node->arg[1]);
}
if (node->name=='*'){
return eval(node->arg[0])*eval(node->arg[1]);
}
if ((node->name>='0')||(node->name<='9')){
return node->name-'0';
}
}

</pre>
[[User:Hlin079|Hlin079]]
.

SE250:lab-8:hlin079 - Revision history

Mark: 5 revision(s)