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  1.  
  2. $ cat new.c
  3. #include <stdbool.h>
  4. #include <stdio.h>
  5. #include <stdlib.h>
  6. #include <string.h>
  8. #define pp(x) printf("%s = %p\n", #x, x);
  9. #define pi(x) printf("%s = %d\n", #x, x);
  10. #define pc(x) printf("%s = %c\n", #x, x);
  12. // A C program to demonstrate linked list based implementation of queue
  13. // A linked list (LL) node to store a queue entry
  14. struct QNode
  15. {
  16. int data;
  17. struct QNode *next;
  18. };
  20. // The queue, front stores the front node of LL and rear stores ths
  21. // last node of LL
  22. struct Queue
  23. {
  24. struct QNode *front, *rear;
  25. };
  27. // A utility function to create a new linked list node.
  28. struct QNode* newNode(int d)
  29. {
  30. struct QNode *temp = (struct QNode*)malloc(sizeof(struct QNode));
  31. temp->data = d;
  32. temp->next = NULL;
  33. return temp;
  34. }
  36. // A utility function to create an empty queue
  37. struct Queue *createQueue()
  38. {
  39. struct Queue *q = (struct Queue*)malloc(sizeof(struct Queue));
  40. q->front = q->rear = NULL;
  41. return q;
  42. }
  44. void store_asm(struct Queue *q, int data)
  45. {
  46. // Create a new LL node
  47. struct QNode *temp = newNode(data);
  49. // If queue is empty, then new node is front and rear both
  50. if (q->rear == NULL)
  51. {
  52. q->front = q->rear = temp;
  53. return;
  54. }
  56. // Add the new node at the end of queue and change rear
  57. q->rear->next = temp;
  58. q->rear = temp;
  59. }
  61. struct QNode * load_asm(struct Queue **q)
  62. {
  63. // If queue is empty, return NULL.
  64. if ((q) == NULL) return NULL;
  65. if ((*q) == NULL) return NULL;
  66. if ((*q)->front == NULL)
  67. return NULL;
  69. // Store previous front and move front one node ahead
  70. struct QNode *temp = (*q)->front;
  71. (*q)->front = (*q)->front->next;
  73. // If front becomes NULL, then change rear also as NULL
  74. if ((*q)->front == NULL)
  75. (*q)->rear = NULL;
  76. return temp;
  77. }
  79. int queue_add(struct Queue **q, int data) {
  80. if (!(*q)) (*q) = createQueue();
  81. store_asm((*q), data);
  82. return 0;
  83. }
  85. struct Queue * list = NULL;
  86. int main(void) {
  87. queue_add(&list, 1);
  88. queue_add(&list, 2);
  89. queue_add(&list, 3);
  90. struct QNode * p = list->front;
  91. while(p) {
  92. printf("%d -> ", p->data);
  93. p = p->next;
  94. }
  95. puts("NULL");
  96. return 0;
  97. }
  99. $ gcc new.c -o new
  102. $ ./new
  103. 1 -> 2 -> 3 -> NULL
  104.  
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