Performing arithmetic with chars in C/C++

Question

How does this C/C++ code work? I understood most of it but not the part specified below:

c2= (c1>='a' && c1<='z') ? ('A'+c1-'a'):c1

Especially this part:

('A'+c1-'a')

What is this part of the code doing?

Both c1 and c2 have type char.

Answer 1

The code converts a lower case character to upper case. If the character isn't lower case then it returns the original character.

The expression ('A'+c1-'a') does the conversion. c1-a will give the 0-based position of the character within the alphabet. By adding this value to A you will get the upper case equivilant of c1.

Update: if c1 is 'b' then the expression c1-'a' would give 1, which is the 0-based position of 'b' in the alphabet' Adding 1 to 'A' will then give 'B'

Answer 2

This part:

('A'+c1-'a')

changes c1 from lower case to upper case.

The whole statement:

c2= (c1>='a' && c1<='z') ? ('A'+c1-'a'):c1

says "if c1 is lower case, change it to upper case and assign that to c2; otherwise, just assign c1 to c2."

Answer 3

char are just integer numbers. You can add do classic operations on them.

The operation will transform (if needed) a lower case char c1 into upper case char. But it is tricky and relies on the ASCII encoding to work and may not work with some specific local.

Instead I recommend using std::toupper, which takes into account the current local to perform the operation