在计算一个表达式的值的程序里: 读入一个完整的数字用到了 char c = cin.peek(); while(isdigit(c)) { result = 10 * result + c - '0';

cin.get();

c= cin.peek(); } 这里的 cin.get();c=cin.peek(); (这里两行) 可以直接用cin >> c; 或者:c=getchar(); 或者:cin.get(c); 一行就代替吗??

不能改~ #include <iostream> #include <cctype>

using namespace std;

int term_value(); int factor_value();

/** Evaluates the next expression found in cin @return the value of the expression. */ int expression_value() { int result = term_value(); bool more = true; while (more) { char op = cin.peek(); if (op == '+' || op == '-') { cin.get(); int value = term_value(); if (op == '+') result = result + value; else result = result - value; } else more = false; } return result; }

/** Evaluates the next term found in cin @return the value of the term. */ int term_value() { int result = factor_value(); bool more = true; while (more) { char op = cin.peek(); if (op == '*' || op == '/') { cin.get(); int value = factor_value(); if (op == '*') result = result * value; else result = result / value; } else more = false; } return result; }

/** Evaluates the next factor found in cin @return the value of the factor. */ int factor_value() { int result = 0; char c = cin.peek(); if (c == '(') { cin.get(); result = expression_value(); cin.get(); // read ")" } else // assemble number value from digits { while (isdigit(c)) { result = 10 * result + c - '0'; cin.get(); c = cin.peek(); //这是改了以后(1+2*3/6 答案2会变成11,但不知为什么) } } return result; }

int main() { cout << "Enter an expression: "; cout << expression_value() << "\n"; system("pause"); return 0; }