You check if a string S is a palindrome by iterating over it from the start and end simultaneously. If at each stage S[index from start] == S[index from end] then you keep going, if they're unequal you know that it isn't a palindrome. If your two indexes meet in the middle then it's indeed a palindrome. How you write a program "fro calciulating avg of 2 nos" I have no idea...