Question

Here is a function for some code im working on in C. Right now it accepts 2 different user inputs and stores them as city and distance. What I want is for the user to input only once. For example "Enter the city name and distance from previous city: Arlington 200". I need to separate that string into values for city and distance. I think I need to use tokens but im not sure how.

void addCity ()
{
char city[30];
int distance;

printf("Enter city name : ");
scanf("%s",city);
printf("Enter distance from previous city: ");
scanf("%d",&distance);
printf("The city has been added.\n");

if(root == NULL){
root = (struct node *) malloc( sizeof(struct node) );
strcpy(root->city, city);
root->distance = distance;
root->next = NULL;
}
else
{

struct node *currentNode = root;
struct node *newNode = (struct node *) malloc( sizeof(struct node) );
while(currentNode->next!=NULL)
{
currentNode = currentNode->next;
}

strcpy(newNode->city, city);
newNode->distance = distance;

currentNode->next = newNode;
}
}

Answer 1

Hello!, Yes you can use tokenize the string using a delimiter. It is a common approach used by developers all around the world. But you will have to be careful when implementing tokenizing since it could easily cause problems when inputting something that is not excepted from the user. I have written a small piece of code so that you understand how to implement tokenization in your code. You can use strtok function in C. It is used for tokenization of the string using delimiters. I have explained the entire code in the comments within the code so that you can understand it easily. Please ask if you have any doubts. I am always available to help you. have a nice day :)

==========tokenizing code using strtok===================

#include <string.h>
#include <stdio.h>
#include <stdlib.h> // we need strlib for using atoi.
int main () {
char city_and_distance[40] = "Arlington 200";
int distance;
char city[30];
const char s[2] = " ";
char *token;

/* You can use strtok to tokenize the string based on the
delimiters.
The syntax is - char *strtok(char *string1, const char *string2);
*/
token = strtok(city_and_distance, s);
strcpy(city, token);

/* get the rest of the tokens. We are basically
looping over the tokens until we obtain a null value.
Basically strtok returns the pointer of the
first token when it counters the delimiter. Then we have to
loop it over to obtain the rest of the tokens.
When it searches for the first token it skips over the rest of the
leading delimiters. And then it returns the pointer. When strtok is
called with a null for string1 argument, the next token is read
from the stored copy of the last non null string1. Then each of the
delimiters is replaced with a null character. */
while( token != NULL ) {
distance = atoi(token); //atoi is basically to convert the string to an integer.
token = strtok(NULL, s);
}

printf("%d\n%s\n", distance , city);

return(0);
}

======================End of tokenizing code====================

As you can see in the above output I have tokenized the string based on a space. You can do the same using any delimiter.

I have also modified your code so that you get an idea of how to implement it into your code.

==================modified code start===============================

void addCity ()
{
char city[30];
int distance;
char city_and_distance[40];
const char s[2] = " "; /* s[2] is the delimiter. you can put any delimiter like ,
or $ for seperating the city and distance.
or you can use a simple space
*/
char *token;

printf("Enter city name and the distance: ");
scanf("%s",city_and_distance);

token = strtok(city_and_distance, s);
strcpy(city, token);

while( token != NULL ) {
distance = atoi(token); //atoi is basically to convert the string to an integer.
token = strtok(NULL, s);
}

printf("The city has been added.\n");

if(root == NULL){
root = (struct node *) malloc( sizeof(struct node) );
strcpy(root->city, city);
root->distance = distance;
root->next = NULL;
}
else
{

struct node *currentNode = root;
struct node *newNode = (struct node *) malloc( sizeof(struct node) );
while(currentNode->next!=NULL)
{
currentNode = currentNode->next;
}

strcpy(newNode->city, city);
newNode->distance = distance;

currentNode->next = newNode;
}
}

===============================Modified code end================================

I assume that this is the way that you implement tokenizing in your code. of course it looks a bit redundant to add tokenization twice. But I have made it so that there is a clear distinction between reading city and distance for your understanding.

Also, I have earlier mentioned about handling the user input can be problematic when using delimiters. The reason is simple. Right now the distance is being read as a string and then being converted into an integer. What if the city had a space like Los Angeles, and the input was Log Angeles 200. Then the program would take the second token which is Angeles and the program would crash. To counter this you can use a delimiter such as "," to separate the city and distance. But if you ask me then the best approach would be to identify the type of the string, i.e if the string or character is a number or not. If it is then store it in distance else store it in city. This is make it more better and you have very less chances of encountering the error. This can be done by using isdigit() which returns 0 if the string value is in [A-Z] or else it returns a random number.