If user enters decimal integer 6, it should give the output F
If user enters decimal integer 7, it should give the output G
If user enters decimal integer 8, it should give the output H
So on and so of for all 26 alphabet
You can use the fact that, in ASCII (which all normal consumer computers use), the capital English letters are contiguous and have numeric, integer values.
For example, 'A' + 1 == 'B'.