Question

我认为我的结构知识缺乏。我收到的错误如下：

pda.c：33：26：错误：'top'未声明（首次使用此功能）
           if（pda.stack [top] =='\ 0'）

pda.c：54：7：错误：'接受'未声明（首次使用此功能）
  if（接受== 0）

pda.c：在函数'qX'中：
  pda.c：93：17：错误：'top'未声明（首次使用此功能）
  pda.stack [top] =输入;

基本上我的全局结构中的变量没有得到识别，我不知道为什么。这是我记录的代码：

//This project is a PDA which accepts alphabetical, lower-case palindromes written out and divided by a #.
//Example: "hello world#dlrow olleh" is an accepted string.
#include <stdio.h>
//Pushdown automata structure includes the string to validate with an index, the stack
//with an index, the current state, the running status, and the result.
struct PDA {
   char string[200];
   char stack[200];
   int current;
   int top;
   int qOrp;
   int finished;
   int accepted;
};
//Initialization of struct and state methods.
struct PDA pda = {.current = 0, .top = 0, .qOrp = 0, .finished = 0, .accepted = 0};
int validateInput();
int qE(char input);
int qX(char input);
int pX(char input);
int pE();

int main() {
   //Prompt for string to validate.
   printf("Enter the string to be verified: ");
   scanf("%s\n", &pda.string);
   //Validates the alphabet of the string.
   pda.finished = validateInput();
   //While the PDA is rinning, do...
   while(pda.finished == 0) {
      //Different cases for different states.
      switch(pda.qOrp) {
         case 0:
            //State for the initial, empty stack.
            if(pda.stack[top] == '\0')
               pda.finished = qE(pda.string[current]);
            //State for non-empty stack before the #.
            else {
               pda.finished = qE(pda.string[current]);
            }
            break;
         case 1:
            //State for empty stack after #.
            if(pda.stack[top] == '\0')
               pda.finished = pE();
            //State for non-empty stack after #.
            else
               pda.finished = pX(pda.string[current]);
            break;
         //Reject if not in one of the states above.
         default:
            pda.finished = 1;
      }
   }
   //Print for acceptance/rejection.
   if(accepted == 0)
      printf("The string \"%s\" is rejected.", pda.string);
   else
      printf("The string \"%s\" is accepted.", pda.string);

   return 0;
}
//Loops through the string to validate and makes sure the alphabet is correct.  Otherwise, reject.
int validateInput() {
   int i = 0;

   while(pda.string[i] != '\0') {
      if(pda.string[i] < 97 || pda.string[i] > 122 || pda.string[i] != '#' || pda.string[i] != ' ')
         return 1;
   }

   return 0;
}
//Initial State.  Checks for illegal characters.  Otherwise, push current character.
int qE(char input) {
   if(input == '#')
      return 1;
   else {
      pda.stack[top] = input;
      pda.top++;
      pda.current++;
      return 0;
   }   
}
//Second State.  Switches to next state on #.  Otherwise, push current character.
int qX(char input) {
   if(input == '#') {
      pda.qOrp++;
      pda.current--;
      pda.top--;
   }
   else {
      pda.stack[top] = input;
      pda.top++;
      pda.current++;
   }
}
//Third state.  Checks for illegal characters.  Otherwise, pop one element from stack.
int pX(char input) {   
   if(input == '#')
      return 1;
   else {
      if(pda.string[current] == pda.stack[top]) {
         pda.stack[top] = '\0';
         pda.top--;
         pda.current--;
      }
      else
         return 1;
   }
}
//Final state.  Declares the string "accepted."
int pE() {
   pda.accepted = 1;
   return 1;  
}

任何想法？感谢。

Answer 1

就像结构中的其他变量一样，top必须使用点表示法作为pda.top进行访问。 accepted必须为pda.accepted。

某些语言有with或using这样的名称范围操作符，但C没有这方面的快捷方式。

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