You can define your own functions in the following way:

function returnType functionName (type1 arg1, type2 arg2,..., typeN argN) {
        variableDeclarations
        otherFunctionDeclarations
        Statements
        Mappings
        return [expression];
    }

You must put the return statement at the end. For more information about the return statement, see Return Statement. Inside some functions, there can be Mappings. These may be in any place inside the function.

In addition to any other data type mentioned above, the function can also return void.

function integer add (integer i1, integer i2) {
    return i1 + i2;
}