calc.cpp

一个简单实用的CMM语言编译器,可以帮助了解如何构造一个简单的词法分析器

/**************************************************
* file: calc.cpp
* date: 2006-06-30
* author: ideawu
* describe: a really small and simple caculator.
*			with known bugs.
**************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "Parser.h"

float calc(SyntaxTree *tree);

int main(int argc, char* argv[]){
	char buf[1024] = "a=";
	SyntaxTree *tree = NULL;
	Lexer *lexer = new Lexer();
	Parser *parser = new Parser();
	
	lexer->setSrc(buf, 1024);
	parser->setLexer(lexer);
	
	printf(">>");
	scanf("%s", &buf[2]);
	while(strcmp(buf, "a=quit") != 0){
		tree = parser->parse();

		if(tree!=NULL){
			//tree->display();
			printf("%g\n", calc(tree->getRight()));
		}else{
			parser->printError();
		}
		printf(">>");
		scanf("%s", &buf[2]);
		parser->reset();
	}

	printf("\n");
	
	return 0;
}

float calc(SyntaxTree *tree){
	float a=0, b=0, val=0;
	
	if(tree != NULL){
		if(tree->getRootNode()->getType() == NUM){
			return tree->getRootNode()->getValue();
		}
		a = calc(tree->getLeft());
		b = calc(tree->getRight());
	
		switch(tree->getRootNode()->getType()){
			case PLUS:
				val = a + b;
				break;
			case MINUS:
				val = a - b;
				break;
			case MUL:
				val = a * b;
				break;
			case DIV:
				if(b != 0){
					val = a / b;
				}
				break;
			default:
				break;
		}
	}

	return val;
	
}