中缀表达式转换成后缀表达式 计算后缀表达式的值 幂操作符添加到你的指令系统中去

数据结构与算法分析——c语言描述 练习3.19 3.20 a b 答案

这道题以前发过文章。现在能支持幂^了。

栈的利用

挺重要的一个思想是 操作符 根据优先级分级

再次更新

1.支持+ - * /  ^

2.支持括号

3.支持括号前后省略*，例如5（4）5=100

4.支持小数点

#include<stack>#include<stdio.h>#include<ctype.h>#include<string>#include<map>using namespace std;#define MAXN 100char expression[MAXN];//输入的表达式string postfix[MAXN];//转换成的逆序表达式int i = 0, j = 0;//i是expression的游标，postfix是逆序表达式的游标map<char, double(*)(double, double)> operaFunc;//运算符字符与运算函数的映射double _add(double x, double y) { return x + y; }double _sub(double x, double y) { return x - y; }double _mul(double x, double y) { return x * y; }double _div(double x, double y) { return x / y; }double _power(double x, double n) {//计算幂次方double ans = 1;for (double i = 0; i < n; i++)ans *= x;return ans;}double operatorCmp(char c1, char c2);//c1为将要插入栈的运算符，c2为栈顶运算符,1表示c1优先级大于c2,0为相等，-1为小于#define putNum()  postfix[j++] = num,num.clear();//把数字输出到逆序表达式#define putOperator() oper= operator_stack.top(),operator_stack.pop(),postfix[j++] = oper;//把符号输出到逆序表达式double operatorPriority(char c) {//运算符优先级比较if (c == '^')return 3;else if (c == '*' || c == '/')return 2;else if (c == '+' || c == '-')return  1;}void ProcessingOperator(char &c,char &oper,string &num, stack<char>&operator_stack) {//i指向的表达是为运算符字符处理if (!num.empty())putNum();if (operator_stack.empty())operator_stack.push(c);else if (operatorCmp(c, operator_stack.top()) >0) {operator_stack.push(c);}else {while (1) {putOperator();if (operatorCmp(c, oper) >0 || operator_stack.empty()) {operator_stack.push(c);break;}}}}int midToPostfix() {//中缀转后缀，返回int是指括号后面是否直接是数字int flag = 0;stack<char>operator_stack;string num;char c, oper;for (; expression[i] != '\0'; i++) {c = expression[i];if (c == '(') {if (isdigit(expression[i - 1]) || expression[i - 1] == ')')//遇到3（4）(3)的情况，要在括号前自行处理省去的*{c = '*';ProcessingOperator(c, oper, num, operator_stack);}i++;if (midToPostfix())//处理(4)4的情况{c = '*';ProcessingOperator(c, oper, num, operator_stack);}continue;}else if (c == ')') {if (isdigit(expression[i + 1]))flag = 1;break;}else if (isdigit(c)||c=='.')num += c;else {//运算符ProcessingOperator(c, oper, num, operator_stack);}}if (!num.empty())//处理表达式最后的数字postfix[j++] = num;while (!operator_stack.empty()) {//处理留在栈的运算符postfix[j++] = operator_stack.top();operator_stack.pop();}if (flag)return 1;elsereturn 0;}double calculatePostfix() {stack<double>num_stack;double x, y, ans;operaFunc['+'] = _add;//添加映射operaFunc['-'] = _sub;operaFunc['*'] = _mul;operaFunc['/'] = _div;operaFunc['^'] = _power;for (i = 0; i < j; i++) {if (isdigit(postfix[i][0]))num_stack.push(stod(postfix[i]));else {//运算符y = num_stack.top();num_stack.pop();x = num_stack.top();num_stack.pop();ans = operaFunc[postfix[i][0]](x, y);num_stack.push(ans);}}return  num_stack.top();}int main() {scanf("%s", expression);midToPostfix();for (int i = 0; i < j; i++) {printf("%s", postfix[i].c_str());}printf("\n");printf("%.3lf", calculatePostfix());}double operatorCmp(char c1, char c2) {double t1, t2;t1 = operatorPriority(c1);t2 = operatorPriority(c2);return t1 - t2;}