A rainbow text color program

[ChimpFace9000]

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....

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;
}

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.

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++;
	};
}

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.

[HarryW]

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:

#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++;
	};
}