虎书P8问题(1)

见《虎书》中文版第８页；
我的答案：

#ifndef P8Q1_H
#define P8Q1_H
#include "slp.h"

int resolveStm(A_stm stm);
int resolveExp(A_exp exp);
int resolveExpList(A_expList expList);
int countExpInExpList(A_expList expList);

#endif

#include "p8q1.h"

int resolveStm(A_stm stm){
    int temp1 = 0, temp2 = 0;
    if(stm->kind == A_compoundStm){
	temp1 = resolveStm(stm->u.compound.stm1);
	temp2 = resolveStm(stm->u.compound.stm2);
	return temp1>temp2? temp1:temp2;
    }else if(stm->kind == A_assignStm){
	return resolveExp(stm->u.assign.exp);
    }else if(stm->kind == A_printStm){// the way out
    	return countExpInExpList(stm->u.print.exps);
    }else{
	return 0;
    }
}

int countExpInExpList(A_expList expList){
    if(expList->kind == A_lastExpList){
	return 1;
    }else if(expList->kind == A_pairExpList){
	return 1 + countExpInExpList(expList->u.pair.tail);
    }else{
	return 0;
    }
}

int resolveExpList(A_expList expList){
    int temp1,temp2;
    if(expList->kind == A_pairExpList){
	temp1 = resolveExp(expList->u.pair.head);
	temp2 = resolveExpList(expList->u.pair.tail);
	return temp1>temp2?temp1:temp2;
    }else if(expList->kind == A_lastExpList){
	return resolveExp(expList->u.last);
    }else{
	return 0;
    }
}

int resolveExp(A_exp exp){
    int temp1,temp2;
    if(exp->kind == A_idExp){
	return 0;
    }else if(exp->kind == A_numExp){
	return 0;
    }else if(exp->kind == A_opExp){
	temp1 = resolveExp(exp->u.op.left);
	temp2 = resolveExp(exp->u.op.right);
	return temp1>temp2?temp1:temp2;
    }else if(exp->kind == A_eseqExp){
	temp1 = resolveStm(exp->u.eseq.stm);
	temp2 = resolveExp(exp->u.eseq.exp);
	return temp1>temp2?temp1:temp2;
    }else{
	return 0;
    }
}

main.c:

#include <stdio.h>
#include "util.h"
#include "prog1.h"
#include "slp.h"
#include "p8q1.h"

main(){
    printf("%d\n",resolveStm(prog()));
}

输出结果：2

体会：对于“目标”需要特殊处理，“目标”就是解析程序的出口。

评论

1 楼 pf_miles 2008-08-16  

上面的代码有缺憾，没有考虑“如果print语句中的expList里面还有print语句”这种情况，需要更改countExpInExpList方法，它也需要和另两个方法互相递归，要解析print语句中的print语句。

int countExpInExpList(A_expList expList){
    int temp1,temp2;
    if(expList->kind == A_lastExpList){
        temp1 = resolveExp(expList->u.last);
        return temp1>1?temp1:1;
    }else if(expList->kind == A_pairExpList){
        temp1 = 1 + countExpInExpList(expList->u.pair.tail);
        temp2 = resolveExpList(expList->u.pair.tail);
        return temp1>temp2?temp1:temp2;
    }else{
        return 0;
    }
}