SE250:lab-8:hpan027

Initial problems

• The error function was called before it was defined and hence needed a prototype declaration.
• "strcmpi" was misspelled as "strcimp"

Task Two

mkNode('-',mkNode('-',mkNode('a',0),mkNode('b',0),0),0);

• Took a while to figure out how to use mkNode

http://studwww.cs.auckland.ac.nz/~hpan027/250-8-1.jpg

• Still can't get the converter to work internally. Had to convert the .dot file manually

Task Three

mkNode('?',mkNode('>',mkNode('+',mkNode('a',0),mkNode('b',0),0),mkNode('c',0),0),mkNode('*',
mkNode('z',0),mkNode('+',mkNode('y',0),mkNode('b',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);

• Is it supposed to be this long?

Task Four

• Cannot even begin to imagine what this would look like

http://studwww.cs.auckland.ac.nz/~hpan027/250-8-2.jpg

• Makes sense
• Horrible quality for some reason ('C', some '-' and some '=' not drawn properly)

Task Five

• Possibly because it expects two set of statements to follow the '?'
• Not really sure at this point

Task Six

• Initial impression: could take a while
• Draft code

int eval( ParseTree* pt ) {
//base case: if + - * /
//evalute number within brackets with the operator
//else eval( subtree )
}

• Very basic code working for single operation between two single-digit integers

int eval( ParseTree* pt ) {
    //base case: if + - * /
    if( pt->arity == 2 )
	switch(pt->name){
	case '+': return atoi(&pt->arg[0]->name)+atoi(&pt->arg[1]->name); break;
	case '-': return atoi(&pt->arg[0]->name)-atoi(&pt->arg[1]->name); break;
	case '*': return atoi(&pt->arg[0]->name)*atoi(&pt->arg[1]->name); break;
	case '/': return atoi(&pt->arg[0]->name)/atoi(&pt->arg[1]->name); break;
	}

    //evalute number within brackets for with the operator
    //else eval( subtree )
}

• This won't work for anything with one or three arguments
• Perhaps base case should be if it is a single integer leaf?
• Turned out to work fine

int eval( ParseTree* pt ) {
    if( atoi(&pt->name) > 0 ) //base case integer leaf
	return atoi(&pt->name);
    else
	switch(pt->name){
	case '+': return eval(pt->arg[0])+eval(pt->arg[1]); break;
	case '-': return eval(pt->arg[0])-eval(pt->arg[1]); break;
	case '*': return eval(pt->arg[0])*eval(pt->arg[1]); break;
	case '/': return eval(pt->arg[0])/eval(pt->arg[1]); break;
	}
}

• However screwed for anything that isn't an operation with two numbers (e.g. -(1+2))
• Although single argument operations would only apply to "-" and "+" - i.e. *(2-3) or /(5) makes no sense
• Use if statements to catch single argument operations?

	case '+': return ( pt->arity>1 ? eval(pt->arg[0])+eval(pt->arg[1]) : eval(pt->arg[0]) );
	case '-': return ( pt->arity>1 ? eval(pt->arg[0])-eval(pt->arg[1]) : -1* eval(pt->arg[0]) );

• Seems to work
• Now need to consider 2+ arguments & if statements?
• If statement would probably be a separate case
• For 2+ argument possibly loop through the whole arg array for values
• Each case statement would probably look something like

case '+': int i=0; int value = 0; for( i = 0; i < pt->arity-1; i++ ) {
	value+=eval(pt->arg[i]);
	return value;

After the lab

Comment on what?

Neat reports.