3. Write a function simulating a calculator on two integer numbers. The function is going to receive a character “op” representing an operation (+,-,*,/,%,etc), “num1” and “num2”. The function is going to check that the input is valid.
If the input is not valid, the function is going to print a corresponding message to the screen and return 0. Otherwise, if the input is valid, then the function should return the result of the operation. For example:
- for op ‘+’ the function is going to return “num1+num2”.
- for op ‘-‘ the function is going to return “num1-num2”.

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