Obtain the SymbolSpec object of the C Function block in your model using get_param. For example, select the C Function block in the model canvas and enter the following at the command line.

mySymbolSpec = get_param(gcb, 'SymbolSpec');

Use the addSymbol function to specify a new parameter symbol, myParam, in your C Function block code.

myParam = addSymbol(mySymbolSpec, 'myParam')

The Symbol object, myParam, uses default properties. Specify the scope of the symbol using the Scope property.

myParam.Scope = 'Parameter';

You can use the getSymbol function to access symbols specified for the block. For example, access the parameter symbol you added.

myParam = getSymbol(mySymbolSpec, 'myParam');

Edit the label of the parameter in the Block Parameters dialog using the Label property.

myParam.Label = 'Amplitude';

To delete a symbol from the SymbolSpec object, use the deleteSymbol function.

deleteSymbol(mySymbolSpec, 'myParam');