usaa20/cv5/a_train.c

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

#include "a_train.h"

struct car* add_car(struct car* first,const char* target) {
    struct car* newcar = calloc(1, sizeof(struct car));
    
    if(target == NULL){
        return 0;
    }
    //if list is empty, then add newcar
    if(first == NULL){
        strcpy(newcar->value, target);
        newcar->next = NULL;
        return newcar;
    }
    strcpy(newcar->value,target);
    newcar->next = NULL;    
    struct car *this = first;

    //find the end of linked list
    while(this->next != NULL){
        this = this->next;         
    }
    
    //add target in the end
    this->next = newcar;
    return first;  
}

void print_train(struct car* first) {
    for(struct car* this = first; this != NULL; this = this->next){
        printf("%s\n", this->value);
    }
}

void cancel_train(struct car* first) {   
    if(first != NULL){
        cancel_train(first->next);
        free(first);
    }
}

struct car* clear_train(struct car* first, const char* target) {
    if(first == NULL){
        return 0;
    } 
    //if there is only one element in linked list, than check if target and value are the same 
    if(first->next == NULL){
      int result = strcmp(first->value, target);
        if(result == 0){
           free(first);
           return 0;          
        }
        else{
            return first;
        }
    }
     
    //check all the elemets in linked list
    struct car* prev = first;
    while(prev->next != NULL){
        int x = strcmp(first->value, target);
        //if the first element and target are the same
        if(x == 0){
            prev = first->next;
            free(first);
            return prev;
            
        }
        x = strcmp(prev->next->value, target);
        //else check all other elements
        if(x == 0){ 
            struct car* third = prev->next->next;
            free(prev->next);
            prev->next = third;    
            return first;            
         
        }
        prev = prev->next;
   }
   return first;
      
}