递归下降语法分析设计原理与实现技术实验报告

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{ case '1': if(token[i]!='(') error1(); break; case '2': if(token[i]!=')') error1(); break; case '3': if(token[i]!='+') error1(); break; case '4': if(token[i]!='-') error1(); break; case '5': if(token[i]!='*') error1(); break; case '6': if(token[i]!='/') error1(); break; case '7': if(token[i]!='i') error1(); break; case '8': if(token[i]!='#') error1(); break; default: error1(); break; } }

void advance() { if(i==MAX) exit(0);

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//读取下一个字符

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current=token[++i]; }

void E() { if(current=='i' || current=='(') { T(); E1(); } else error(); }

void E1() { if(current=='+' || current=='-') { A(); T(); E1(); } else if(!(current==')' || current=='#')) error(); }

void T() { if(current=='i' || current=='(') { F(); T1(); } else error(); }

void T1() { if(current=='*' || current=='/') { M(); F();

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T1(); } else if(!(current==')'||current=='#'||current=='+'||current=='-')) error(); }

void M() { if(current=='*') advance(); else if(current=='/') advance(); else error(); }

void A() { if(current=='+') advance(); else if(current=='-') advance(); else error(); }

void F() { if(current=='(') { advance(); E(); if(current==')') advance(); } else if(current=='i') advance(); else error(); }

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void error() { cout<<\ exit(0); }

void error1() { cout<<\输入错误！\ exit(0); }

int main() { int flag; //提供输入和文件两种方式 int j=1; int i=0; char token1[MAX]; //用于检测文件输入是否匹配 FILE *fp; cout<<\输入方式：键盘(1)/文件(2):\ while(!(cin>>flag) || (flag!=1 && flag!=2)) { cout<<\ cin.clear(); cin.ignore(200,'\\n'); } if(flag==1) { cout<<\请输入长度不超过50且以#结束的字符串：\ cin>>token; } else { if((fp=fopen(\ { cout<<\文件打开失败！\ exit(0); } token1[0]=fgetc(fp); while(!feof(fp)) { token1[j++]=fgetc(fp); if((j%5)==0)

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}

{ token2[i]=token1[j-4]; token[i]=token1[j-2]; justify(token2[i],i); i++; } } if((j-1)%5 != 0) error1(); cout<<\读入字符串为：\} init(); E();

if(current=='#') cout<<\return 1;

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