How to add two hexadecimal strings and get total in third string?

Question

I have two strings which are hex value for some number now I want to add them and want the result in the hex values which is also a string.

Answer 1

It is unclear what is important in your question: you could have been given the task of implementing "string addition" (maybe a student assignment?); or you could simply have two numbers which are represented as strings and need to form their sum and represent it as a string.

In the first case you need to loop over the two strings a character at a time, produce the digit sum, calculate the carry, etc. For checking a character is a valid hex digit and converting it into a value you can sum you should look at the functions isxdigit(), ishexnumber() and digittoint() - all these are part of the standard (Objective-)C library and the documentation can be found using the man command in the Terminal. For computing the sum and carry you will find the modulus operator, %, useful or you could consider using div(). To convert your individual digit sum back to a character you can use a string of hex digit characters and simply index into it.

In the second case you can stick with Objective-C framework classes: NSScanner provides methods to parse hex numbers; and NSString's stringWithFormat: enables you to convert a number to a hex representation. In this case addition is just the normal operator, +, as the numbers are in standard internal format (i.e. binary bits).

If you have trouble implementing either approach ask a new question, showing your code and describing your issue, and someone will undoubtedly help you.

HTH