Question

I have a program that contains the following piece of code for constructing an array of asterisks:

char array[Length][Height];

for (int count1 = 1; count1 <= Length; count1++)
{
    for (int count2 = 1; count2 <= Height; count2++)
    {
        strcpy(array[count2][count3], "*");
        cout << array[count2][count3];
    }
}
cout << endl;

When I attempt to compile the program, I receive the following output:

waves.cpp:48: error: invalid conversion from ‘char’ to ‘char*’
waves.cpp:48: error: initializing argument 1 of ‘char* strcpy(char*, const char*)’

The ‘char*’ part of the output lead me to do some reading on pointers, and while I understand the basic principle of them, actually implementing them is proving somewhat difficult (and I guess that’s the difference between reading about something and doing it).

If someone could tell me where I’m going wrong in this code so I could use it as a worked example, it would go a long way to helping me understand the use of pointers.

Answer 1

Try this:

char array[Length][Height];

for (int count1 = 0; count1 < Length; count1++)
{
    for (int count2 = 0; count2 < Height; count2++)
    {
        array[count1][count2] = '*';
        cout << array[count1][count2];
    }
}
cout << endl;

Note that your code contained off-by-one errors: count1 and count2 would go from 1 to Length/Height, which would skip the first byte in the array and write one byte past its size. In C/C++, array indices start at zero and end at length – 1. I corrected the errors in the code above.

strcpy() is intended for copying strings from one place in memory to another. What you want to do is not to copy a string, but to assign a single char value (which, conceptually, is no different from an int apart from its size*). The C language has no native string type — instead, it uses continuous blocks of memory that end with a byte that has the value zero (null-terminator). Working with strings in this manner is difficult, painful and error-prone. Since your post is tagged with “c++”, I would advise you to use the C++ Standard Library’s string type when dealing with strings in the future.

* On some platforms, an int might be no larger than a char.