# How to find the middle letter among the specified letters?

I’ve created a function that accepts 2 parameters to find the middle value between those parameters in an `Alphabet` variable.

Example:

``````the middle part between Q and U is S,
the middle part between R and U is ST,
the middle part between T and Z is W,
``````

What I’m confused about is how do I take the value one by one starting at index 1 in the `Alphabet` variable?

``````function letterMiddleValue(a, b) {
let alpha1 = Alphabet.indexOf(a);
let alpha2 = Alphabet.indexOf(b);
let center = (alpha1 + alpha2) / 2;
let letterLength;

if (center % 2 == 1) {
letterLength = 1;
} else {
letterLength = 2;
}
return Alphabet.substring(center, center + letterLength);
}

var Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

console.log(letterMiddleValue("Q", "U"));
console.log(letterMiddleValue("R", "U"));
console.log(letterMiddleValue("T", "Z"));``````

### >Solution :

Center for r & u is 18.5. 18.5 % 2 is 0.5 so you need to check for 0.5 condition:

``````function letterMiddleValue(a, b) {
let alpha1 = Alphabet.indexOf(a);
let alpha2 = Alphabet.indexOf(b);
let center = (alpha1 + alpha2) / 2;
let letterLength;

if (center % 2 == 0.5) {
letterLength = 2;
} else {
letterLength = 1;
}

return Alphabet.substring(center, center + letterLength);
}

var Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

console.log(letterMiddleValue("Q", "U"));
console.log(letterMiddleValue("R", "U"));
console.log(letterMiddleValue("T", "Z"));
``````

That’s because how you calculate center.
(7 + 5) / 2 = 6.5
(6 + 10) / 2 = 8
and modulo gives back what’s not dividable by 2