Program to find the factorial of a number

Factorial says to multiply all whole numbers from the chosen number down to 1. The mathematical symbol of Factorial is "!" 

Examples:

4! = 4 × 3 × 2 × 1 = 24 

7! = 7 × 6 × 5 × 4 × 3 × 2 × 1 = 5040

we get all the possible output and our program work correctly ie when we enter posititve number then only we get factorial, if we enter negative number then we get respective output which is defined in program