# 3 Problem Example

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3.1 Description

A common interoperability situation is when you want to incorporate a piece of code, solving a complex problem, in your Erlang program. Suppose for example, that you have the following C functions that you would like to call from Erlang:

    /* complex.c */

    int foo(int x) {
      return x+1;
    }

    int bar(int y) {
      return y*2;
    }

The functions are deliberately kept as simple as possible, for readability reasons.

From an Erlang perspective, it is preferable to be able to call foo and bar without having to bother about that they are C functions:

    % Erlang code
    ...
    Res = complex:foo(X),
    ...

Here, the communication with C is hidden in the implementation of complex.erl. In the following sections, it is shown how this module can be implemented using the different interoperability mechanisms.