编译原理

题目

借助于词法分析程序提供的分析结果，编写一个算符优先语法分析程序，程序能进行语法结构分析和错误检查，并产生相应的归约信息。

思路

1. 找到等式的右边
2. 转换为输入字符串
3. 对输入字符串进行分析，即归约、移进、接受这三个操作。

代码

/** * Created by luopu on 2017/6/8. */package 编译原理实验二;import java.util.*;@SuppressWarnings("unused")public class A {    static int no=0;    static int[][] jilu=new int[10][10];    static int index=0;    static String[] oper={            ">", ">", "<", "<", "<", ">", "<", ">",            ">", ">", "<", "<", "<", ">", "<", ">",            ">", ">", ">", ">", "<", ">", "<", ">",            ">", ">", ">", ">", "<", ">", "<", ">",            "<", "<", "<", "<", "<", "=", "<", "e",            ">", ">", ">", ">", "e", ">", "e", ">",            ">", ">", ">", ">", "e", ">", "e", ">",            "<", "<", "<", "<", "<", "e", "<", "="};    static Stack<String> stk = new Stack<String>();    static int ans=1;    public static String contentsOf(Stack<String> stk) {        String str=stk.toString();        str=str.replace("[", "");        str=str.replace("]", "");        str=str.replace(",", "");        str=str.replace(" ", "");        return str;    }    public static void printStates(String str, String op) {        String current=str.substring(0, 1);        String rest=str.substring(1, str.length());        String action="移进";        if(op==">") {            jilu[no][index++]=ans;            action="归约";        }        if(op=="="&&rest.length()==0) {            action="接受";        }        System.out.printf("%5d%10s%7s%10s%15s%5s\n", ans++,contentsOf(stk),op,current,rest,action);        if(action.equals("接受")) {            System.out.print("归约产生式步骤号为：");            for(int i=0; jilu[no][i]!=0; i++) {                System.out.print(jilu[no][i]+" ");            }            index=0;            System.out.println("\n");        }    }    public static int numOf(String str) {        switch(str) {        case "+": return 0;        case "-": return 1;          case "*": return 2;        case "/": return 3;        case "(": return 4;        case ")": return 5;        case "i": return 6;        case "#": return 7;        }        return 8;    }    public static void second(String str) {        stk.clear();        ans=1;        stk.push("#");        int k=0, r=0, i=0;        String op="";        for(;;) {            // 得到k， r的值            for(i=0; i<10; i++) {                k=numOf(stk.get(stk.size()-1-i));                if(k!=8) {                    r=numOf(str.substring(0, 1));                    break;                }            }            // 得到优先关系符            op=oper[k*8+r];            // 归约? 移进？接受？            if(op.equals(">")) {                // 归约                printStates(str, op);                for(;i>0;i--) {                    stk.pop();                }                for(;;) {                    stk.pop();                    k=numOf(stk.lastElement());                    if(k!=8&&!oper[k*8+r].equals("e")) {                        break;                    }                }                stk.push("N");            } else {                // 移进                printStates(str, op);                stk.push(str.substring(0, 1));                str=str.substring(1, str.length());                if(op.equals("=")&&str.length()==0) {                    // 接受                    break;                }            }        }    }    public static void first(String str) {        System.out.println("算术表达式"+(++no)+"为："+str);        try {            int a=Integer.parseInt(str);            str="i#";        } catch (Exception e) {            String newStr="";            for (int i = 0; i < str.length(); i++) {                if(0<=(str.charAt(i)-'0')&&(str.charAt(i)-'0')<=9) {                  newStr+="i";              } else {                  newStr+=str.charAt(i);              }            }            str=newStr+"#";        }        System.out.println("转换为输入串："+str);        System.out.println("步骤号    符号栈    优先关系     当前分析符    剩余字符串  动作");        second(str);    }    public static void main(String[] args) {        String str="b=100 101:a=2*(1+3) IF (b>10) THEN a=1 ELSE IF(b>=5) THEN a=2 ELSE GOTO 101";        String fenxiStr="";        for (int i = 0; i < str.length(); i++) {            if(str.charAt(i)=='='&&str.charAt(i-1)!='>') {                i++;                for(;i<str.length(); i++) {                    if(str.charAt(i)!=' ') {                        fenxiStr+=str.charAt(i);                    } else {                        first(fenxiStr);                        fenxiStr="";                        break;                    }                }            }        }    }}

结果

PERFECT！！！