A rainbow text color program

Recently there was talk about a program that will create a rainbow effect using html code. So i thought id try making my own. The problem is i keep getting an illegal operation error whenever i run it. I think the problem is in this function....

Code:

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void GenerateCode(char *String, char *Buffer)
{
        int sLength = strlen(String);       
        int Total = White - Black;
        int IncAmount = Total / sLength;
        int Count = 1;
        int Color = Black;
        while(Count <= sLength)
        {
                strcat(Buffer, "<FONT COLOR=\"");
                strcat(Buffer, (const char*)Color);
                strcat(Buffer, "\">");
                strcat(Buffer, (const char*)String[Count]);
                strcat(Buffer, "</FONT>");
                Color = Color + IncAmount;
                Count++;
        }
        return;
}

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If you see a problem in there please let me know, i havent used C++ in a while so i might be forgetting something. Ive also included the full source for those who want to see it.

Code:

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void GenerateCode(char *String, char *Buffer)
{
        int sLength = strlen(String);       
        int Total = White - Black;
        int IncAmount = Total / sLength;
        int Count = 1;
        int Color = Black;
          Buffer = new char[29 * sLength + 5];
        while(Count <= sLength)
        {
                strcat(Buffer, "<FONT COLOR=\"");
                strcat(Buffer, (const char*)Color);
                strcat(Buffer, "\">");
                strcat(Buffer, (const char*)String[Count]);
                strcat(Buffer, "</FONT>");
                Color = Color + IncAmount;
                Count++;
        };
}

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You haven't allocated any memory for Buffer, and you're trying to assign stuff to it.. 29 * sLength is because the length of each <FONT C...></FONT> tag is 29 characters.. and there will be sLength sets of the FONT tag....the + 5 just assures there is enough space in Buffer... you don't need the return; statement either... the function is void. You also need a semicolon after the while-loop.

It's far easier to do this with the STL string class, if you're using C++. Otherwise, if you're using straight C, you'll need to use malloc() or realloc() or somethig like that to allocate the memory.

Dennis, ya i did, i did it earlier in the code. Its a buffer that can be used at any time.

Have you tried my code?

I'm just a lil' curious to see if it works.

To use the STL string class just do:

Code:

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#include <string>
using namespace std;
//.
//..
//...

void GenerateCode(string String, string Buffer)
{
        int sLength = String.length();       
        int Total = White - Black;
        int IncAmount = Total / sLength;
        int Count = 1;
        int Color = Black;
        Buffer = "";
        while(Count <= sLength)
        {
                Buffer += "<FONT COLOR=\"";
                Buffer += (const char*)Color;
                Buffer += "\">";
                Buffer += String.substr(Count,1);
                Buffer += "</FONT>";
                Color = Color + IncAmount;
                Count++;
        };
}

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