用栈实现中缀表达式向后缀表达式的转换

  1 #include <stdio.h>
  2 #include <stdlib.h>
  3 
  4 typedef struct Node
  5 {
  6     char ele;
  7     struct Node * next;
  8 }Node;
  9 
 10 typedef Node * Stack;
 11 
 12 Stack MakeStack(void)//新建栈并返回栈顶
 13 {
 14     Stack S = (Node *)malloc(sizeof(Node));
 15     S->next = NULL;
 16     return S;
 17 }
 18 
 19 void MakeNUll(Stack S)//置空栈
 20 {
 21     S->next = NULL;
 22 }
 23 
 24 void Pop(Stack S)//将栈顶弹出
 25 {
 26     Stack temp = S->next;
 27     S->next = temp->next;
 28 }
 29 
 30 void Push(Stack S, char c)//将新节点压入栈
 31 {
 32     Stack temp = (Node *)malloc(sizeof(Node));
 33     temp->ele = c;
 34     temp->next = S->next;
 35     S->next = temp;
 36 }
 37 
 38 Stack FindHead(Stack S)//返回栈顶
 39 {
 40     Stack temp = S->next;
 41     return temp;
 42 }
 43 
 44 void PrintHead(Stack S)//打印栈顶元素
 45 {
 46     Stack temp = S->next;
 47     printf("%c", temp->ele);
 48 }
 49 
 50 int main(void)
 51 {
 52     Stack S = MakeStack();
 53     int i = 0;
 54     char str[200];
 55     printf("Type something.\n");
 56     gets(str);
 57 
 58     while(str[i] != ‘\0‘)
 59     {
 60         if(str[i] == ‘+‘ || str[i] == ‘-‘)//如果str[i]是加号或减号，则先弹出栈顶直到栈已空或栈顶元素为左括号，再将str[i]压入栈
 61         {
 62             if(FindHead(S) == NULL)//若栈已空时，栈顶指针为空，找不到其元素，故须单独讨论
 63             {
 64                 Push(S, str[i]);
 65             }
 66             else
 67             {
 68                 while(FindHead(S)->ele == ‘+‘ || FindHead(S)->ele == ‘-‘ || FindHead(S)->ele == ‘*‘ || FindHead(S)->ele == ‘/‘)
 69                 {
 70                     PrintHead(S);
 71                     Pop(S);
 72                 }
 73                 Push(S, str[i]);
 74             }
 75         }
 76 
 77         else if(str[i] == ‘*‘ || str[i] == ‘/‘)//如果str[i]是乘号或除号，则只有栈顶也是乘除号时才需要弹出
 78         {
 79             if(FindHead(S) == NULL)
 80             {
 81                 Push(S, str[i]);
 82             }
 83             else
 84             {
 85                 while(FindHead(S)->ele == ‘*‘ || FindHead(S)->ele == ‘/‘)
 86                 {
 87                     PrintHead(S);
 88                     Pop(S);
 89                 }
 90                 Push(S, str[i]);
 91             }
 92         }
 93 
 94         else if(str[i] == ‘(‘)//如果str[i]是左括号则直接压入栈
 95         {
 96             Push(S, str[i]);
 97         }
 98 
 99         else if(str[i] == ‘)‘)//如果str[i]是右括号，则打印并弹出栈中第一个左括号前的所有操作符，最后将此左括号直接弹出
100         {
101             while(FindHead(S)->ele != ‘(‘)
102             {
103                 PrintHead(S);
104                 Pop(S);
105             }
106             Pop(S);
107         }
108 
109         else//如果str[i]不是操作符则直接打印
110         {
111             printf("%c", str[i]);
112         }
113 
114         i++;
115     }
116 
117     while(FindHead(S) != NULL)//遍历后如果栈不为空，则弹出所有操作符
118     {
119         PrintHead(S);
120         Pop(S);
121     }
122 
123     return 0;
124 }