Calculate and print the sum of the perfect squares less than $2000$

$($A perfect square is a number that can be expressed as the product of two equal integers. i$.$e$.$ a number whose square root is an integer, e$.$g$.9$ is a perfect square since$)$

Write a function which takes two array with the same size. The $i^{th}$ element of the second array should be the average of the first i element of the first array

$3.$ Write a C program to find the factorial of each element in an array of $10$ elements and store the results in another array. Read the array elements from user keyboard. Then calculate the summation of all elements and print it$.$

$4.$ Write a $C$ code using pointers to read a string from user. Then Remove all characters except alphabets. For example if the input string is $656$ff$"$:jj$!$@$$ the result should be $"$ffjj$"$