What does #define CHAR_TO_INDEX(c) ((int)c-(int)'a') mean?

Answer 1

look up for ASCII table, here you will see distance between a and n equals 13 :)

Answer 2

It is a macro definition

CHAR_TO_INDEX(c) accepting a character argument.

(int)c - returns the index of character represented by c
(int)'a' - returns the index of character 'a'

hence
((int)c-(int)'a') - returns the distance between value in c and letter 'a'

#include <iostream>
#define CHAR_TO_INDEX(c) ((int)c - (int)'a')

using namespace std;

int main (){
cout<<CHAR_TO_INDEX('n'); //returns 13
}

Answer 3

how does it returns 13?

Answer 4

thanx