You can set predefined Fibonacci levels by using enumerations. Either you use enumerations provided by MQL5 or define your own, like this:
//+------------------------------------------------------------------+
//| Enumeration for Fibonacci levels |
//+------------------------------------------------------------------+
enum ENUM_FIBO_LEVELS
{
fib0618 = 0618, // 61.8%
fib1000 = 1000, // 100.0%
fib1382 = 1382, // 138.2%
fib1618 = 1618, // 161.8%
};
Note: If you place a single-line comment, it will be associated with the variable name, as shown in this example.
input ENUM_FIBO_LEVELS FiboValue=fib1618; // Fibonacci level
As a result, users are able to select their preferred Fibonacci level:

To calculate potential support and resistance levels, convert the Fibonacci ENUM
level:
(double(FiboValue)/1000)
If you have any further questions, please leave a comment below.