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我認爲我的結構知識是缺乏的。我得到的錯誤如：下推自動機的結構問題
- pda.c:33:26: error: 'top' undeclared (first use in this function)
if(pda.stack[top] == '\0')- pda.c:54:7: error: 'accepted' undeclared (first use in this function)
if(accepted == 0)- pda.c: In function 'qX':
pda.c:93:17: error: 'top' undeclared (first use in this function)
pda.stack[top] = input;
基本上我的全局結構中的變量沒有被識別，我不知道爲什麼。這裏是我記錄的代碼：
//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？謝謝。