c,validation,input,while-loop,linked-list , How to make sure user input is unique


How to make sure user input is unique

Question:

Tag: c,validation,input,while-loop,linked-list

in my program I want to make sure that the 'identifier' String the user inputs is unique, for a new Book object they are creating. I think a While loop is the way to go , and have it keep asking the user to input a an identifier until it doesn't match an existing one. Really struggling to find a way to make it work, so if anyone can point me in the right direction i'd really appreciate it. Thanks!

Im using a Linked List structure by the way..

void addBook(){
struct node *aNode;
struct book *aBook;
struct node *current, *previous;
bool identifierIsTaken = true;

char identifierInput[10];

current = previous = front;

aBook = (struct book *)malloc(sizeof(struct book));


    while(identifierIsTaken){           
    printf("Enter identifier for new book: ");
    scanf("%s", identifierInput); 

    if(!strcmp(identifierInput, current->element->identifier) == 0){
        identifierIsTaken = false;
        strncpy(aBook->identifier, identifierInput, 10);
    }
    else
        previous = current;
        current = current->next;
    }

    printf("Enter book name: ");
    scanf("%s", &aBook->name);

    printf("Enter author: ");
    scanf("%s", &aBook->author);

..........

The loop seems to work only once when I enter an occupied identifier, but then if I try again it falls through and the identifier is taken.


Answer:

It's better to write a separate function to check identifier is unique or not.

int isUnique(char *identifierInput,struct node start)
{
    while(start != NULL) {   
        if(strcmp(identifierInput, start->element->identifier) == 0) {
          //string already present,return 0.
          return 0;
        }
        start = start->link;
    }   
    //we reached end of linked list.string is unique.return 1.
    return 1;
}

From your main you call this function,

sudo code

int main()
{
    :
    :
    :
    while(i<number_of_item){
        printf("Enter identifier for new book: ");
        scanf("%s", identifierInput); 
        if(isUnique(identifierInput,current)){
            //add it to the linked list.do whatever you want here.
        } else {
            // it is not unique.do what ever you want here.
        }
    }
    :
    :
    :
}

Hope it will be helpful.


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