前缀式计算

  1 #include <stdio.h>  2 #include <string.h>  3 #include <stdlib.h>  4 #include <math.h>  5 typedef struct stack{  6     double data;  7     struct stack *next;  8 }stack;  9 stack *init(); 10 int isOperand(char ch); 11 stack *push_stack(stack *top, double data); 12 stack *pop_stack(stack *top); 13 void calc(stack **top, char ch); 14 int main() 15 { 16     char ch[5001], temp[1000]; 17     stack *top; 18     top = init(); 19     double num; int i, count, flag, j; 20     while(gets(ch) != NULL) 21     { 22         i = strlen(ch) - 1; 23         while(i >= 0) 24         { 25             if(ch[i] == ‘ ‘)//判断如果是空格，继续下一个 26             { 27                 i --; 28                 continue; 29             } 30             if(isOperand(ch[i]))//如果是运算符，这是调用计算函数 31             { 32                 calc(&top, ch[i]); 33                 i --; 34                 continue; 35             } 36             count = 0; flag = 1; j = 0; 37             while(!isOperand(ch[i]) && ch[i] != ‘ ‘ && i >= 0)//判断是数字的话就保存到一个新的数组中 38             { 39                 temp[j++] = ch[i]; 40                 i --; 41             } 42             j = j -1; 43             num = 0; 44             while(j >= 0)//将字符串解析成double类型数字 45             { 46  47                 if(temp[j] == ‘.‘) 48                 { 49                     flag = 0; 50                     j --; 51                     continue; 52                 } 53                 if(flag) 54                     num = num * 10 + (temp[j] - ‘0‘);//如果没出现小数点之前，都是*10 + 本身的 55                 else 56                 { 57                     count ++; 58                     num += pow(0.1, count) * (temp[j] - ‘0‘);//出现小数点之后就得加上0.1的count此方了 59                 } 60                 j --; 61             } 62             top = push_stack(top, num); 63         } 64         printf("%.2f\n", top -> data); 65     } 66     return 0; 67 } 68 stack *init()//初始化栈 69 { 70     stack * node; 71     node = (stack *)malloc(sizeof(stack)); 72     node -> next = NULL; 73     return node; 74 } 75 int isOperand(char ch)//判断是不是运算符 76 { 77     if(ch == ‘+‘ || ch == ‘-‘ || ch == ‘*‘ || ch == ‘/‘) 78         return 1; 79     return 0; 80 } 81 stack *push_stack(stack *top, double data)//入栈 82 { 83     stack *node; 84     node = init(); 85     node -> data =http://www.mamicode.com/ data; 86     node -> next = top; 87     top = node; 88     return top; 89 } 90 stack *pop_stack(stack *top)//出栈 91 { 92     stack *node; 93     node = top; 94     top = top -> next; 95     free(node); 96     return top; 97 } 98 void calc(stack **top, char ch)//计算函数，当然也可以不用二级指针，把void改成stack返回类型  就行了 99 {100     double num1, num2;101     num1 = (*top) -> data;102     (*top) = pop_stack(*top);103     num2 = (*top) -> data;104     (*top) = pop_stack(*top);105     switch(ch)106     {107     case ‘+‘:108         num1 = num1 + num2;109         break;110     case ‘-‘:111         num1 = num1 - num2;112         break;113     case ‘*‘:114         num1 = num1 * num2;115         break;116     case ‘/‘:117         num1 = num1 / num2;118         break;119     }120     (*top) = push_stack(*top, num1);//计算完之后将结果继续入栈121 }