The factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n. The function uses for loop to calculate the factorial and returns the number. Program terminates if a non integer number is entered. This C language program uses for loop in just a single statement to calculates the factorial of integer number.
5!= 5 x 4 x3 x2 x1 =120

Fibonacci series , 0 , 1 , 1 , 2 , 3 , 5 , 8 , 13 , 21 , 34 ………Fibonacci sequence are the numbers in the following integer sequence 0 , 1 , 1 , 2 , 3 , 5 , 8 , 13 , 21 , 34 ……… By definition, the first two numbers in the Fibonacci sequence are 0 and 1, and each subsequent number is the sum of the previous two.

Interchange the elements of an array
Interchange the elements of an arrays is to exchange the elements of both the array with each other
A. [5]=1,2,3,4,5 B. [5]=6,7,8,9,10
After Exchange :-
A. [5]= 6,7,8,9,10 B. [5]= 1,2,3,4,5

A natural number greater than one has not any other divisors except 1 and itself. In other word we can say which has only two divisors 1 and number itself. For example: 5
Their divisors are 1 and 5.
Logic for prime number in c
We will take a loop and divide number from 2 to less than number. If the number is not divisible by any of the numbers then we will print it as prime number.