easiest way to get Decimal to Hex in c++?

Does this work for you?

http://www.codeproject.com/cpp/baseconvert.asp

Try this link:
http://www.gidforums.com/t-2615.html
They have very good comments and explanation.

I am assuming you want to do this for display purposes - for any other purpose there is not really a conversion because 0xFF = 255 = 11111111.

Output to the console

printf ( "%x", decimalnumber) ;

save to a string

sprintf ( str, "%x", decimalnumber ) ;

If your decimal number (and integer) is in a string first convert the number to an int, then format the variable to another string

char pInteger[] = "256"; //my integer string
char pHex[256]; //destination string
int nValue;

if( sscanf( pInteger , "%d" , &nValue ) == 1 ) //returns number of converted elements
{
   sprintf( pHex , "0x%08x" , nValue );
}

=> pHex now holds "0x00000100"

CString has a Format() function that doest excactly what sprintf() does, in case you use MFC. Also if your source string is in a CString, you can use it as the first parameter in the sscanf() statement, because CString's can be seen as const char*'s

leave the "0x", and the "08" if you dont want the prefix and the 0-padding and the 8 characters wide field

Just a minor point - if you are going to convert from a string you could also use atoi or atol

char dec[] = "1234" ;
char hex[10] ;
int x ;

x = atoi ( str ) ;
sprintf ( hex, "0x%08x", x ) ; // adopting Ruskialt's formatting options here