how to read a const char* from keyboard input and perform strlen() on it?

Question

So I have been trying for 1.30 hour to get this to work. I am new indeed, but I have searched all over the place and couldn't find an exact answer. I do not wish to do this another way, as it would take away the entire purpose of learning to code. I have to find why this thing isn't working. I tried dozens if not hunderds of syntaxes, but nothing works.

I want to read in a const char* name, than count the number of elements in it, so I thought had to be strlen(), and than output the name and the number of elements. If that works I can write the rest of the code.

#include <iostream>

using namespace std;

int main()
{
    //writing your name, and counting the characters including \0
    int a;
    const char* name;

    a = int strlen(name);

    cin.getline(name);

    cout << name;
    cout >> a;

    return 0;
}

Answer 1

There are a lot of problems with your code.

You are not allocating any memory for cin.getline() to read into. const char* name; is declaring an uninitialized pointer to nothing. You have to allocate memory for name before you can then read any data into it.

cin.getline() expects two input parameters (a pointer to an allocated buffer, and the max number of characters the buffer can hold), but you are only passing in one value.

You are calling strlen() before you have read anything into name (and there is a syntax error on your strlen() statement anyway).

You are passing a to std::cout using >>, but std::ostream does not implement the >> operator. You have to use << instead.

And lastly, don't use using namespace std;.

Try this instead:

#include <iostream>
#include <cstring>

int main()
{
    //writing your name, and counting the characters including \0
    int a;
    char name[32];
    
    std::cin.getline(name, 32);
    a = std::strlen(name);

    std::cout << "You entered: " << name << std::endl;
    std::cout << "It is << a << " chars in length" << std::endl;

    return 0;
}

Or, if you really don't like using std:: everywhere, at least use using <identifier>; instead of using namespace std;:

#include <iostream>
#include <cstring>

using std::cin;
using std::strlen;
using std::cout;
using std::endl;

int main()
{
    //writing your name, and counting the characters including \0
    int a;
    char name[32];
    
    cin.getline(name, 32);
    a = strlen(name);

    cout << "You entered: " << name << endl;
    cout << "It is " << a << " chars in length" << endl;

    return 0;
}

Now, that being said, the preferred solution is to use std::getline() instead of cin.getline():

#include <iostream>
#include <string>
    
int main()
{
    int a;
    std::string name;
    
    std::getline(std::cin, name);
    a = name.length();

    std::cout << "You entered: " << name << std::endl;
    std::cout << "It is " << a << " chars in length" << std::endl;

    return 0;
}

Answer 2

I found a working solution, although I don't see where I had gone wrong. But this does exactly what I want using const char* and strlen() without using std::string.

Thanks for all your help, you have all pointed me to the correct direction.

#include <cstdio>
#include <cstring>
#include <iostream>

using namespace std;

int main ()
{
   const char *name;
   int len;

   name = "stephane";

   len = strlen(name);
   cout << name;
   cout << len;

   return(0);
}

Answer 3

As another user has pointed out, I think it's a good idea for you to take a few steps back and read the basics until you understand how pointers work.

A const char* is that: const. It could be used usually while doing things like this:

const char* cpName = "Stephane"; //expected not to change through the program's lifetime
char* pName = "Stephane"; //can be changed to point to something else
char *pOther = "Vada";
pName = pOther; //pName now points to the string "Vada"
cpName = pOther; //this won't compile as cpName is const