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Watching your code, realized that you declared the function Fdelta() receiving 3 parameters inteiros, and when you will use you are not passing the parameters, this error refers to missing parameters in the function Fdelta(), for you to solve, put: Fdelta(A, B, C);, so you will be passing the values of A, B and C as a parameter for the function.

Could you copy the code? So we could test it
– Codigo de Senior