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  1. #include <iostream>
  2. #include <string>
  3. using namespace std;
  4.  
  5. struct node {
  6. 	int value;
  7. 	node * next;
  8. 	node * previous;
  9. 	node(int v, node * n = NULL) {
  10. 		value = v;
  11. 		previous = next;
  12. 		next = n;
  13. 	}
  14. };
  15.  
  16. struct chain {
  17. 	node * head;
  18. 	chain(node * h = NULL) {
  19. 		head = h;
  20. 	}
  21. 	~chain() {
  22. 		clear();
  23. 	}
  24. 	int push(int v) {
  25. 		head = new node(v, head);
  26. 		return v;
  27. 	}
  28. 	int pop() {
  29. 		int v = head->value;
  30. 		node * n = head;
  31. 		head = head->previous;
  32. 		delete n;
  33. 		return v;
  34. 	}
  35. 	int back() {
  36. 		return head->value;
  37. 	}
  38. 	void clear() {
  39. 		while(head != NULL) {
  40. 			node * n = head;
  41. 			head = head->next;
  42. 			delete n;
  43. 		}
  44. 	}
  45. 	int size() {
  46. 		int size = 0;
  47. 		for(node * i = head; i != NULL; i = i->next) size++;
  48. 		return size;
  49. 	}
  50. 	bool empty() {return head == NULL;}
  51. } stack;
  52.  
  53. int main() {
  54. 	string s;
  55. 	while (cin >> s) {
  56. 		if (s == "exit") {cout << "bye\n" << head->previous; return 0;}
  57. 		if (s == "push") {int x; cin >> x; stack.push(x); cout << "ok\n";}
  58. 		if (s == "pop") 
  59. 			if (stack.empty()) cout << "error" << endl;
  60. 			else cout << stack.pop() << endl;
  61. 		if (s == "back") 
  62. 			if (stack.empty()) cout << "error" << endl;
  63. 			else cout << stack.back() << endl;
  64. 		if (s == "clear") {stack.clear(); cout << "ok\n";}
  65. 		if (s == "size") {cout << stack.size() << endl;}
  66. 	}
  67. }
Compilation error #stdin compilation error #stdout 0s 5420KB
comments (?)
stdin
copy 
push 1
push 2
push 3
pop
front
exit
compilation info 
prog.cpp: In function ‘int main()’:
prog.cpp:56:40: error: ‘head’ was not declared in this scope
   if (s == "exit") {cout << "bye\n" << head->previous; return 0;}
                                        ^~~~
prog.cpp:56:40: note: suggested alternative: ‘fread’
   if (s == "exit") {cout << "bye\n" << head->previous; return 0;}
                                        ^~~~
                                        fread
stdout
copy 
Standard output is empty
https://ideone.com/lXsLJv
https://w...content-available-to-author-only...p.com/ru/problems/6124
language:
C++14 (gcc 8.3)
created:
2 years ago
visibility:
public

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