Letter to number and number to letter

[21vXjE8b]

Maybe this is a homework question, but I can't find a way of solving it...
In my code, you put a message to be codified (hello), put a key value (e.g. 3) and the result is KHOOR (3 letters forward).
The problem is that the code is long. I did 52 If statements! So I need to simplify it!
Each letter has a number, like A = 1, B = 2, ... , Z = 26. It adds to these numbers the value of the key value (if the result is more than 26, it subtracts 26). If the final result is 1, we have A; 2, we have B; ... ; 26, we have Z.

for (i=0; i < msgToEncrypt.length(); i++) {
		
		if (msgToEncrypt[i] == 'A' || msgToEncrypt[i] == 'a') a = 1;
		if (msgToEncrypt[i] == 'B' || msgToEncrypt[i] == 'b') a = 2;
		if (msgToEncrypt[i] == 'C' || msgToEncrypt[i] == 'c') a = 3;
                ...
                if (msgToEncrypt[i] == 'Z' || msgToEncrypt[i] == 'z') a = 26;
		
		b = a + key_value;
		
		if (b > 26) b -= 26;
		
		if (b == 1) c = 'A';
		if (b == 2) c = 'B';
		if (b == 3) c = 'C';
                ...
                if (b == 26) c = 'Z';
		
		cout << c;
}

I wanna know if there's a command that change letter to number and number to letter, replacing the 52 If statements!

[TheIdeasMan]

Realise that a char is just a small int, so you can do math with it:

char MyChar = 'A';
char EncyptedChar = MyChar +3;  // is character 'D', using ASCII 

Hope this helps !!

[48T7M4Gy]

Might like to throw in modular arithmetic there too, in order to stay within the bounds of whatever alphanumeric system is chosen and therefore avoid non-printing characters especially.

[48T7M4Gy]

.

[21vXjE8b]

Thank you TheIdeasMan! That helped me a lot!
I noticed that kemort... But, how can I apply modular arithmetic in this case?

char c, i;
string msgToEncrypt;

for (i=0; i < msgToEncrypt.length(); i++) {
		
		c = msgToEncrypt[i] + key_value;
				 
		cout << c;
}

[48T7M4Gy]

.

[48T7M4Gy]

https://en.wikipedia.org/wiki/Caesar_cipher

[21vXjE8b]

Got it!!! Thank you!