mecanum joystick selector?

[Devo1098]

i have a mini mecanum bot, im trying to program it (programming is not my area, building is)

i need it to do single stick drive , then when i click the trigger of that stick, and move the stick sideways, the robot will go sideways.

i thought it would need two drive codes one for sideways and one for skidsteer, and a simple if statment between them.(this didnt work)

im pretty shure my concept works, i jsut need a little help putting it into code, could someone translate this into C, or shoot me in the right direction? or if this is the totally wrong way to do this, help?

IF (trigger pushed in)
then (do sideways code)
otherwise (do skid steer code)

Devo

Edit: i dont need mixing values or mecanum code, im having trouble with a selector.