how to initialize a stateflow??

i have few parameters that should be executed at the starting of the model for example,let a=2,b=3,This is the initial values.If mode is 1 it should take inputs c and d else it should take a=c,b=d then add them .

This is the sample int a=2,b=3,mode,c,d,e; it should ask for mode...then we enter the mode,depending onthe mode value it should execute as i told above.... the output of this model is given to another model..so the values a,b should be initialized only once,like that of call back in simulink

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