问总线错误: 10在struct指针C上使用malloc

EN

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

int main(){

    struct name{
        char *first;
        char *last;
    };

    struct name *user;

    char temp[10];

    printf("What is your first name?\n");
    scanf("%s", temp);
    user->first = (char*) malloc(strlen(temp)+1);
    strcpy(user->first, temp);

    printf("What is your last name?\n");
    scanf("%s", temp);
    user->last = (char*) malloc(strlen(temp)+1);
    strcpy(user->last, temp);

    printf("Your name is %s %s\n", user->first, user->last);

    free(user->first);
    free(user->last);

    user->first = NULL;
    user->last = NULL;

}