执行代码 c++
#include
#include
using namespace std;
enum Token_value{
NAME, NUMBER, END,
PLUS = '+', MINUS = '-',MUL = '*',DIV = '/',
PRINT = ';',ASSIGN = '=',LP = '(',RP = ')'
};
Token_value curr_tok = PRINT;
// fuction list//////////////////////////////////////
double expr(bool get);
double term(bool get);
double prim(bool get);
Token_value get_token();
double error(const string &s);
//////////////////////////////////////////////////////////
double expr(bool get) //plus and minus
{ double left = term(get);
for(;;)
{ switch(curr_tok){
case PLUS:
left+=term(true);
break;
case MINUS:
left-=term(true);
break;
default:
return left;
}
}
}
double term(bool get) // multiply and divide
{ double left = prim(get);
for(;;)
{ switch(curr_tok){
case MUL:
left*=prim(true);
break;
case DIV:
if(double d = prim(true)){ // no zero!!
left/= d;
break;
}
return error("divide by zero!!\n");
default :
return left;
}
}
}
double number_value;
double string_value;
double prim(bool get)
{ if(get) get_token();
switch(curr_tok){
case NUMBER:
{ double v = number_value;
get_token();
return v;
}
case NAME:
{ double v;
//double &v = table[string_value];
//this table reserved the name mapped with variable
//now we don't use it!
if(get_token()==ASSIGN)
v = expr(true);
return v;
}
case MINUS: // negative
{ return -prim(true);
}
case LP:
{ double e = expr(true);
if(curr_tok!=RP)return error(")expected");
get_token(); // absorb )
return e;
}
default:
return error("primary expected"); // no primary
}
}
Token_value get_token()
{ char ch =0;
cin>>ch;
switch(ch){
case 0:
return curr_tok=END; //return and assignment
case ';':
case '*':
case '/':
case '+':
case '-':
case '(':
case ')':
case '=':
return curr_tok = Token_value(ch);
case '0':case '1':case '2':case '3':case '4':
case '5':case '6':case '7':case '8':case '9':
case '.':
cin.putback(ch);
cin>>number_value;
return curr_tok = NUMBER;
default:
if(isalpha(ch))
{ cin.putback(ch);
cin>>string_value;
return curr_tok = NAME;
}
error("bad token!");
return curr_tok = PRINT;
}
}
int no_of_error;
double error(const string &s)
{ no_of_error++;
cout<<"error:"<
return 1;
}
int main()
{ while(cin)
{ get_token();
if(curr_tok==END)break;
if(curr_tok==PRINT) continue;
cout<
}
return no_of_error;
}
¥29.8
¥9.9
¥59.8