How can I create a BST by reading from a text file? - c

Question

I have to create a database of students, that contains their ID, name, surname, and grade. This information is read from a txt file that looks like this:
AE797989 Spears Michael 10.00
AA566734 Walsh Brad 10.00
AE808090 Jones Dimitris 5.00
...
and contains 19 students
I have to read each line of the file and create a binary search tree based on their ID. There seems to be a problem when I'm creating a node, because when I try to search a student I can't. Here's my code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
struct node
{
struct node *left;
char ID[100];
char NAME[100];
char LAST_NAME[100];
float Grade;
struct node *right;
};
struct node *newNode(char, char, char, float);
struct node *insertNode(struct node node, char id, char name, char last_name, float grade);
void search(struct node *root, char *ID);
void deleteFromBST(char *ID);
int main()
{
char ID[100];
int insertDone = 0;
int ch;
while (1) {
printf("\n1. Insertion\t2. Deletion\n");
printf("3. Searching\t4. Display In Order\n5. Edit\t 6. Exit\n");
printf("Enter your choice:");
scanf("%d", &ch);
switch (ch) {
case 1:
if (insertDone)
puts("Inserton was already done");
else {
struct node* insertNode(struct node *node,char *id, char *name, char *last_name, float grade)
{
if (node == NULL)
return newNode(*id,*name,*last_name,grade);
if ( strcmp(id , node->ID) < 0)
node->left = insertNode(node->left,id,name,last_name,grade);
else if ( strcmp( id , node->ID) >= 0)
node->right = insertNode(node->right,id,name,last_name,grade);
return node;
}
insertDone = 1;
}
break;
case 2:
break;
case 3:
printf("Enter the AM to search:");
scanf("%99s", ID);
void search(struct node *root, char *ID)
{
int flag=0;
if (!root)
{
printf("Search element unavailable in BST\n");
return;
}
while (root != NULL) {
if (strcmp(root->ID, ID) == 0) {
printf("Student ID : %s\n", root->ID);
printf("First Name : %s\n", root->NAME);
printf("Last Name : %s\n", root->LAST_NAME);
printf("grade : %lg\n", root->Grade);
flag = 1;
break;
}
else if (strcmp(ID , root->ID) > 0)
{
return search(root->right,ID);
}
else if(strcmp(ID , root->ID) < 0)
{
return search(root->left,ID);
}
if (!flag)
printf("Search element unavailable in BST\n");
}
}
break;
case 4:
//display();
break;
case 5:
break;
case 6:
exit(0);
default:
printf("U have entered wrong option!!\n");
break;
}
}
struct node* newNode(char *id, char *name, char *last_name, float grade)
{
struct node *newnode = malloc(sizeof(struct node));
struct node Node;
FILE *fp;
fp = fopen ("Foitites-Vathmologio-DS.txt","rb");
if (fp == NULL)
{
fprintf(stderr,"Could not open file");
return;
}
char line[4096];
while (fgets(line, sizeof line,fp))
{
size_t len = strlen(line);
if (len && (line[len - 1] == '\n'))
{
/* incomplete line */
if (sscanf(line,"%99s %99s %99s %f",Node.ID, Node.NAME, Node.LAST_NAME, &Node.Grade) != 4)
{
puts("invalid file");
return;
}
strcpy(newnode->ID , id);
strcpy(newnode->NAME , name);
strcpy(newnode->LAST_NAME , last_name);
newnode->Grade = grade;
newnode->left = newnode->right = NULL;
return newnode;
}
}
fclose(fp);
}
return 0;
}
I get no error messages.. thank you for your time!

Answer 1

If you get no error message with this code, I would suggest you to use a different compiler. Mine chokes in main at:
switch (ch) {
case 1:
if (insertDone)
puts("Inserton was already done");
else {
struct node* insertNode(struct node *node, char *id, char *name,
char *last_name, float grade) // ERROR HERE
{
if (node == NULL)
It looks that you have copied the definition of the function instead of just calling it.
My problem is that you managed to write many different errors in a single program. And the global design of how the program should be structured is not clear: it looks like you started coding without first writing on a paper (yes papers and pencils are still very good tools for beginners) what each function should do, what was its its inputs and what should be its outputs and eventually what data it was including (for example what part is in charge of the file name). Of course, I could write a BST program for you, but you would not learn anything from that.
So here are some hints:
in a BST, you insert new data under existing nodes so you will need a function insertNode with following input parameters: the current root node (or NULL at first time), the id, name, last_name and grade to insert. You should build a new copy of the input strings (strdup is your friend). This function will allocate a new structure, fills is fields, and either return it if the current root was NULL, or insert it at its correct place in the existing tree
you want to process all lines from a file. You will need a function that open the file, read it line by line and will use previous one to insert the new record in the BST
BTW a function definition is something like
struct node *insert(struct node *root, const char id*, const char *name, const char *last_name, float grade) {
struct node * newnode = malloc(sizeof *newnode);
...
return root;
}
outside of any other function definition, while a function call will be like:
struc node *root = NULL;
char id[100], name[100], last_name[100];
float grade;
...
if (sscanf(line,"%99s %99s %99s %f",id, name, last_name, &grade)) != 4)
{
puts("invalid file");
return;
}
root = insert(root, id, name, last_name, grade); // here is the function call