If the value you enter consists entirely of valid hexadecimal characters, it is treated as a hexadecimal value unless it is also the name of a variable that is currently in scope. For example, suppose you have a variable feedbeef, and you enter "feedbeef" as a register value. If the variablefeedbeef can be represented as a hex value, that hex value is used. Otherwise, the debugger uses the hex value "feedbeef". To force the debugger to use a hex value rather than the contents of a variable, precede the hex value with "0x" (for example, "0xfeedbeef").
For C++, you can also enter a segmented address, or an expression. Numbers used in the expression are treated as decimal unless explicitly preceded with "0x".