Sample

H file :

typedef struct {
    double angle;
    double force;
} PhysicsInput;

typedef struct {
    double airTime;
    double travelDistance;
} SimulationOutput;

typedef struct {
    double targetDistance;
    double distanceWeight;
    double airtimeWeight;
} ObjectiveParams;

SimulationOutput simulatePhysics(const PhysicsInput& input);
double objectiveFunc(const PhysicsInput& input, const ObjectiveParams& target);


C file :

#include <math.h>
#include "func.h"

SimulationOutput simulatePhysics(const PhysicsInput& input)
{
    SimulationOutput output;
    output.airTime = sin(input.angle) * input.force * 9.8 / 2;
    output.travelDistance = output.airTime * cos(input.angle);
    return output;
}

double objectiveFunc(const PhysicsInput& input, const ObjectiveParams& target)
{
    SimulationOutput out = simulatePhysics(input);
    double retVal = 0;
    double distanceFromTarget = (out.travelDistance - target.targetDistance);
    retVal += distanceFromTarget * distanceFromTarget * target.distanceWeight;
    retVal += target.airtimeWeight * out.airTime;
    return retVal;
}