Thread: Question on "Jumping into C++" Chapter 13 practice problem 1

Hi Everybody,

This is my first time posting to this board, so hopefully my question is formulated properly. I'm having problems with Chapter 13 practice problem 1. Basically, we have to write a function which prompts the user to enter first and last names and return the user's full name to main. This has to be done using pointers, since this is the chapter on pointers. Anyway, here is what I got so far:

Code:

#include <iostream>

using namespace std;

void return_names(char *p_first, char *p_last)
{
    char first, last;
    cout << "Please enter the first name: ";
    cin >> first;
    cout << "Please enter the last name: ";
    cin >> last;
    *p_first = first;
    *p_last = last;
}

int main()
{
    char first_name, last_name;
    return_names(&first_name, &last_name);
    cout << "The full name is: " << first_name << " " << last_name;
    return 0;
}

The problem is that my code will only read in one character for first and last name. I tried using a char array, but couldn't get it to work for some reason. Can somebody give me a clue how this can be done using pointers? My problem is I don't know how to read in the entire name. Thanks in advance for your help!

Ben

The problem is that my code will only read in one character for first and last name.

That's because you used a char as the type, this can only hold one character.

I tried using a char array, but couldn't get it to work for some reason.

First you should be using C++ strings not C-strings. And if you're having problems you need to show the code that is causing the problem, and then describe the problem. Also remember that the extraction operator>> will stop processing your string when it encounters any whitespace character.


Jim

Hence the bonus question :-P
We'll just have to disagree on the didactics part.

Hi Everybody,

Thanks so much for your help so far. I will respond to one of the replies and then show the code where I see my error.

Jiggunjer, I tried running your code and it works, but I'm not sure why. In the book, he hasn't done stuff like this...

Code:

void getnames(char*& p)
{
  cin>>nameone; //includes '\0' at the end
  p=nameone;//assign our pre-sized array to ptr1
}

Why do you do char*& p? I'm not sure what the "&" is there for.

Here is my attempt at using a char array, but I'm getting an error. I will post the code along with the error.

Code:

#include <iostream>

using namespace std;

void return_names(char *p_first, char *p_last)
{
    char first[20], last[20];
    cout << "Please enter the first name: ";
    cin >> first;
    cout << "Please enter the last name: ";
    cin >> last;
    p_first = first;
    p_last = last;
}

int main()
{
    char first_name[20], last_name[20];
    return_names(&first_name, &last_name);
    cout << "The full name is: " << first_name << " " << last_name;
    return 0;
}

Here is the error:

cannot convert 'char (*)[20]' to 'char*' for argument '1' to 'void return_names(char*, char*)'|
||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

I don't really understand this error. Can somebody give me a clue how my code could be modified so that it works?

Also, in my original code, for the return_names function, I wrote this:

Code:

*p_first = first

However, it seems once I modified it to use the char array I got an error when I tried dereferencing p_first and assigning it to first, so I got rid of the '*' and the error went away. Why is that?

Thanks,
Ben

The & means pass by reference. This is the way most void returning functions manage to manipulate variables from a different scope (like main in this case).

Code:

void function1(int A) //makes a copy of the int passed to it and calls it A
void function2(int &A) //Uses the original integer from wherever it was called, no new variable A is created in memory.

as for your last remark

However, it seems once I modified it to use the char array I got an error when I tried dereferencing p_first and assigning it to first, so I got rid of the '*' and the error went away. Why is that?

now you are assigning an array to a pointer (valid)
before you were assigning a char to the contents of a char pointer--i.e. char to char (valid)
when you changed "first" from char to array it would be assigning an array to char (not valid)