嘗試在C中使用掃描值創建二進制搜索樹

Question

我遇到了很多麻煩。我已經看了很多例子和類似的實現，我仍然無法弄清楚爲什麼這不起作用。出於某種原因，我的代碼正在獲取每個新值並使其成爲新的頭，並從本質上刪除上一棵樹。除了插入值，它說的頭是空每次和重寫存儲於頭價值...以下是我的代碼：

typedef struct studentRec{ 
    int id; 
    char name[25]; //the name has a maximum length of 25 letters 
    char major[15]; //the major array has a max length of 15 
    int year; 
    struct studentRec *left, *right; 
}student; 

student* createNode(int ID, char *name, char *major, int year); 
student* initBST(FILE *input, char *argv); 
student* addNode(student *head, int ID, char *name, char *major, int year); 
int Search(student *head); 
void printInorder(student *n); 


int main(int argc, char *argv[]){ 
FILE *input; 
printf("This is the name of input: %s\n", argv[1]); 
student *mainHead = malloc(sizeof(student*)); 
mainHead = initBST(input, argv[1]); 
printInorder(mainHead); 
return 0; 
} 

student* initBST(FILE *input, char *argv){ 
    int ID = -1; 
    input = fopen(argv, "r"); 
    fscanf(input, "%d", &ID); 
    student *head = malloc(sizeof(student*)); 
    int grade = -1; 
    while(ID != 0){ 
     char *first, *last, *major, *name; 
     first = malloc(25*sizeof(char)); 
     last = malloc(25*sizeof(char)); 
     major = malloc(25*sizeof(char)); 
     name = malloc(25*sizeof(char)); 
     fscanf(input, "%d", &ID); 
     if(ID == 0){ 
     break; 
     } 
     fscanf(input, "%s %s %s %d", first, last, major, &grade); 
     sprintf(name, "%s %s", first, last); 

     head = addNode(head, ID, name, major, grade); 
    } 
    return head; 
} 

void printInorder(student *n){ 
    if(n != NULL){ 
     printInorder(n->left); 
     printf("This is the current value of ID: %d\n", n->id); 
     printInorder(n->right); 
    } 
} 

student* createNode(int ID, char *name, char *major, int year){ 
      printf("Adding this ID value: %d\n", ID); 
      student *new = malloc(sizeof(student*)); 
      new->left = NULL; 
      new->right = NULL; 
      new->id = ID; 
      strcpy(new->name, name); 
      strcpy(new->major, major); 
      new->year = year; 
      return new; 
} 

student* addNode(student *head, int ID, char *name, char *major, int year){ 
    if(head == NULL){ 
     printf("head == NULL\n"); 
     return createNode(ID, name, major, year); 
    } 
    else{ 
     if(ID < head->id){ 
      return head->left = addNode(head->left, ID, name, major, year); 
     } 
     else if(ID > head->id){ 
      return head->right = addNode(head->right, ID, name, major, year); 
     } 
    } 
} 

Answer 1

似乎ADDNODE第一次調用正常工作和創建頭。然而，當initBST調用ADDNODE第二次，ADDNODE這兩行的一個重複出現：

if(ID < head->id){ 
     return head->left = addNode(head->left, ID, name, major, year); 
    } 
    else if(ID > head->id){ 
     return head->right = addNode(head->right, ID, name, major, year); 
    } 

由於兩個頭戴式>左，頭戴式>右邊是NULL，ADDNODE的新的迭代將打印你的頭= = NULL消息，但它會正確創建新節點。 addNode的另一個迭代（運行上面的代碼）正確地設置了head-> left或head->，但它然後返回該值，initBST將其設置爲新的頭部。 addNode的相關部分應如下所示：

head->left = addNode(head->left, ID, name, major, year); 
return head; 
// with the other one changed as well