Searching for values inside a linked list in C

Question

I have created a program in C where a CSV file consisting of coordinates and location IDs is inserted into a linked list. Now I want to create a separate function that prints out all location IDs where the x coordinate is equal to 20 or greater. However my program isn't printing out any values at all for some reason. How do I fix this?

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

#define MAX 10

struct data {
    double x, y, id;
    struct data *next;
}*head;                                                         

typedef struct data data;

void read_csv();
void search();

int main(int argc, char *argv[]) {
    read_csv();
}

void read_csv() {
    // Opens the CSV datafile
    FILE *fp = fopen("data.csv", "r");
    
    char buffer[MAX];
    struct data** tail = &head;
    
    while (fgets(buffer, MAX, fp)) {
        data *node = malloc(sizeof(data));
        node->x = atof(strtok(buffer, ","));
        node->y = atof(strtok(NULL, ","));
        node->id = atof(strtok(NULL, ","));
        node->next = NULL;
        *tail = node;
        tail = &node->next;
  
    }
    search();
}

void search() {
    struct data *temp;
    temp = head;
    while(temp!=NULL) {
        if (temp->x >= 20) {
            printf("%lf\n",temp->id);
            temp = temp->next;
        }
    }
}

Here is the CSV input file:

19.743748,-11.838155,0.947989
19.810734,-11.838155,0.947972
19.877850,-11.838155,0.947953
19.945097,-11.838155,0.947930
20.012476,-11.838155,0.947904
20.079988,-11.838155,0.947875
20.147631,-11.838155,0.947844
20.215405,-11.838155,0.947812
20.283312,-11.838155,0.947780                   

Answer 1

temp = temp->next; must be outside the if clause.

void search() {
    struct wake *temp;
    temp = head;
    while(temp!=NULL) {
        if (temp->x >= 20) {
            printf("%lf\n",temp->id);
        }
        temp = temp->next;
    }
}