//implement a calculator //no bracket #include <iostream> #include<cctype>//the ‘isdigit‘ which was included in it will be used in the funcion named number; #include <cstdlib> using std::cin; using std::cout; using std::endl; void eatspaces(char * str); double number(const char * str, size_t & index); double expr(const char *str); double term(const char *str, size_t & index); int main() { const int max{ 80 };//length of the expression char buffer[max]{}; cout << endl << "enter an expression , or an empty line to quit :" << endl; while (1) { cin.getline(buffer, sizeof buffer);//get an expression from keyboard cout << "the expression you enter is : " << buffer<<endl; eatspaces(buffer); cout << "the expression without spaces is : " << buffer << endl; double value{}; //size_t index{}; value = expr(buffer);//calculate the expression //value = number(buffer, index);//be use to test whether the function "number" is on work cout << "the value :" << value << endl; if (buffer[0] == 0) return 0; } //cout << endl; return 0; } /*expr :calculate the expression got from buffer*/ double expr(const char *str) { double value{}; size_t index{};//this index will be used from now to the end ,which show as a ‘&‘ //divide the expression into term according to the ‘+‘ or ‘-‘ value=term(str, index);//the beginning term for (;;) { char temp{ *(str + index) }; index++; cout << "test index" << endl; switch (temp) { case ‘\0‘:return value; case ‘+‘: value = value + term(str, index); break;//whether put index++ here or not? case ‘-‘:value = value - term(str, index); break; //default:char message[38]{ "expression evaluation error,found: " }; // strncat_s(message, str + index -1, 1); // throw message; // break; } } } /*calculate every term by using the multi (*)and divide(/)*/ double term(const char *str, size_t & index) { double value{}; value = number(str, index); while (1) { if (*(str + index) == ‘*‘) value = value*number(str, ++index); else if (*(str + index) == ‘/‘) value = value / number(str, ++index); else break; //switch (*(str + index++)) //{ //case ‘\0‘:return value; //case ‘*‘:value = value*number(str, index); break; //case ‘/‘:value = value / number(str, index); break; //default:return value; //} } return value; } /*read number;*/ double number(const char * str, size_t & index) { double value{}; while (isdigit(*(str + index))) { value = 10 * value + (*(str + index) - ‘0‘); index++; } if (*(str + index) != ‘.‘) { return value;//if the number is not a decimal } else { //if the number is a decimal double factor{ 1.0 }; index++;//point to the char after the dicimal while (isdigit(*(str + index))) { factor = factor*0.1; value = value + (*(str + index) - ‘0‘)*factor; index++; } return value; } } /*delete space*/ void eatspaces(char * str) { size_t i{};//control the pointer which point to the new string; size_t j{};//control the pointer which point to the old string; do { if (*(str + j) != ‘ ‘) { *(str + i) = *(str + j); i++; } j++; } while (*(str + j) != ‘\0‘); *(str + i) = ‘\0‘;//give an end command to the new string ; return; }
时间: 2024-10-10 02:54:35