Question

My problem is very simple, but I really don’t know how to manipulate strings in C

The problem is:
I have a struct called person

struct person
{
  char name[25] // use char *name better?
}p;

I also have a function called p *addNewPerson(char *name)

p *addNewPerson(char *name)
{
  p *newPerson = (p *)malloc(sizeof(person));
  //here how can I assign the name to this new person?
  ...
  return newPerson;
}

So, in the main function

void main()
{
   for(; ;)
  {
    char input[25];
    scanf("%s", input); // is this way possible?
    //shoud I do something with this "input", like input[strlen(input)-1] = '\0'
    //call addNewPerson()
    p *newPerson = addNewPerson(&input);
    //store this newPerson in some data structure
    ...
  }
}

Clarification: the question is how can I assign the name to this new person inside p *addNewPerson(char *name)?

Answer 1

p *newPerson = (p *)malloc(sizeof(person));
//here how can I assign the name to this new person?

You would do this:

strcpy(p->name,name);

You should also change your use of p to struct person since p is not a type, it is a global veriable of type struct person . Change the code to:

struct person *addNewPerson(char *name)
{
   struct person *newPerson = malloc(sizeof *newPerson);

//shoud I do something with this
“input”, like input[strlen(input)-1] =

No, scanf will nul terminate the string for you.

Be aware though, string handling in C needs to be done very, very carefully.
e.g. when you do scanf("%s", input); , what happens if you enter a name longer than 24 characters ?

Anything might happen. scanf might overflow your buffer, and you get undefined behavior. You should do atleast this:

  int ret = scanf("%24s",buffer);  //read max 24 chars, to make space for a final '\0'
  if(ret == EOF) { //end of input reached.
     break; 
  if(ret != 1) {
    // for whatever reason, the conversion failed. exit, or alert the user, or whatever
  }

Similarly inside your addNewPerson at the strcpy(p->name,name); , strcpy might happily write past
the buffer if the name is longer than what p->name can hold. In this particular case, with the above modification to scanf, the length will always be 24 or less so it’s safe. But be very aware of this in general .

The call to addNewPerson should just pass the name of buffer directly, when used as a value, the name of an array decays to a pointer to the first element of that array;

 struct person *newPerson = addNewPerson(input);

Since newPerson is dynamically allocated with malloc() , remember to free() it when you no longer need it. Otherwise you will leak memory.