C语言算数表达式识别器功能增强 - 支持数字识别和错误提示

#include <stdio.h> #include <stdlib.h> #include <string.h> #include using namespace std; char str[100]; int index = 0; void E(); // E->TX; void X(); // X->+TX|-TX|^ void T(); // T->FY void Y(); // Y->*FY|/FY|^ void F(); // F->(E) | i int count; int m, n; int len;

void rank1() { printf("%d\t", count); count++; }

void analyze() { if (m < 0) cout << ' '; else { for (int i = 0; i <= m; i++) cout << str[i]; } cout << '\t' << '\t' << '\t'; }

void latter() { printf("%c", str[index]); cout << '\t' << '\t' << '\t'; }

void remain() { for (int j = n + 1; j <= len; j++) cout << str[j]; cout << '\n'; }

/* 文法G[E]: E → E+T | E-T | T T → T*F | T/F | F F → (E) | i | num 消除左递归后： E → TX X → +TX|-TX|^ T → FY Y → *FY | /FY|^ F → (E) | i | num */

void error() { printf("错误位置：%d\n", index + 1); printf("错误信息：无效字符\n"); exit(0); }

void number() { rank1(); printf("F -> num\t\t"); analyze(); while (str[index] >= '0' && str[index] <= '9') { latter(); index++; } m++; n++; remain(); }

int main() { count = 0; m = -1, n = -1; index = 0; printf("请输入算数表达式："); scanf("%s", str); len = strlen(str); str[len] = '#'; printf("步骤\t 文法\t\t 分析串\t\t\t分析字符\t\t剩余串\n"); E(); if (str[index] == '#') printf("是\n"); else { printf("否\n"); error(); } return 0; }

void E() { rank1(); printf("E -> TX\t\t"); analyze(); if (str[index] >= '0' && str[index] <= '9') { number(); } else { latter(); index++; remain(); T(); X(); } }

void X() { if (str[index] == '+') { index++; rank1(); printf("X ->+TX\t\t"); m++; n++; analyze(); latter(); remain(); T(); X(); } else if (str[index] == '-') { index++; rank1(); printf("X ->-TX\t\t"); m++; n++; analyze(); latter(); remain(); T(); X(); } else { rank1(); printf("X -> ^\t\t"); analyze(); latter(); remain(); } } void T() { rank1(); printf("T -> FY\t\t"); analyze(); if (str[index] >= '0' && str[index] <= '9') { number(); } else { latter(); index++; remain(); F(); Y(); } } void Y() { if (str[index] == '*') { index++; rank1(); printf("Y ->*FY\t\t"); m++; n++; analyze(); latter(); remain(); F(); Y(); } else if (str[index] == '/') { index++; rank1(); printf("Y ->/FY\t\t"); m++; n++; analyze(); latter(); remain(); F(); Y(); } else { rank1(); printf("Y -> ^\t\t"); analyze(); latter(); remain(); } } void F() { if (str[index] >= '0' && str[index] <= '9') { number(); } else if (str[index] == 'i') { index++; rank1(); printf("F ->i\t\t"); m++; n++; analyze(); latter(); remain(); } else if (str[index] == '(') { index++; rank1(); printf("F ->(E)\t\t"); m++; n++; analyze(); latter(); remain(); E(); if (str[index] == ')') { index++; rank1(); printf("F ->(E)\t\t"); m++; n++; analyze(); latter(); remain(); } else { printf("否\n"); error(); } } else { printf("否\n"); error(); }