C语言实现简单算术表达式解析器

#include <stdio.h> #include <ctype.h>

char lookahead;

void error() { printf("FOUND ERROR"); exit(1); }

void match(char expected) { if (lookahead == expected) { lookahead = getchar(); } else { error(); } }

void E(); void T(); void F();

void E() { T(); while (lookahead == '+') { match('+'); T(); } }

void T() { F(); while (lookahead == '') { match(''); F(); } }

void F() { if (isdigit(lookahead)) { match(lookahead); } else if (isalpha(lookahead)) { match(lookahead); } else if (lookahead == '(') { match('('); E(); match(')'); } else { error(); } }

int main() { printf("Enter an arithmetic expression # : "); lookahead = getchar(); E(); if (lookahead == '#' && getchar() == '\n') { printf("SUCCESS"); } else { error(); } return 0; }

// Example input: # i1*( i2+i3)# // Output: SUCCESS