change C# type to c++

The question, as it is stated, makes no sense. You are not talking about C++/CLI, but about C++, which target native platforms, not .NET. Most types are different and cannot be compared; they don't work together anywhere beyond P/Invoke.

Your question makes sense only in one aspect: types are function parameters. When you call a C++ function using P/Invoke, some types are marshaled. By default, a by-value char* (char[]) parameter is marshaled as System.String, and by reference parameter is marshaled as System.Text.StringBuilder. (This is because System.String is immutable; and System.Text.StringBuilder can be considered as a mutable version of string.)

—SA

C++ Type C# Type Size
BOOL bool 1 byte
BYTE byte 1 byte
CHAR byte 1 byte
DECIMAL Decimal 16 bytes
DOUBLE double 8 bytes
DWORD uint, UInt32 4 bytes
FLOAT float, single 4 bytes
INT, signed int int, Int32 4 bytes
INT16, signed short int short, Int16 2 bytes
INT32, signed int int, Int32 4 bytes
INT64 long, Int64 8 bytes
LONG int, Int32 4 bytes
LONG32, signed int int, Int32 4 bytes
LONG64 long, Int64 8 bytes
LONGLONG long, Int64 8 bytes
SHORT, signed short int short, Int16 2 bytes
UCHAR, unsigned char byte 1 byte
UINT, unsigned int uint, UInt32 4 bytes
UINT16 ushort, UInt16 2 bytes
UINT32, unsigned int uint, UInt32 4 bytes
UINT64 ulong, UInt64 8 bytes