simplest way to "route" messages

I am sending values over serial from max. I have single chars being handled with if/else statements in arduino. What I want is a simple messaging/labeling system. I am aware of the many libraries that do this and much much more for me. But I just want to know the code of how to do it without an external library, as I am still trying to learn the basics here. Thanks for the help.

from max these are some example messages
a222
z235
s124

I would like to:
"if the first char is a then set the value[a] to 222"
if the first char is z then set the value of [z] to 235

etc.

How would I go about achieving this. To let you know where I am coming from attached is the static version I have running:

if (Serial.available() > 0){ // Check serial buffer for characters
char ch = Serial.read();
//Serial.println ('ch');

if (ch == 'a') { // If an 'r' is received then run the motor
dc1.setSpeed (250); // This is where I would like the value 250 instead to come from a longer input message ie. a250
dc1.run(FORWARD); // turn it on going forward
// Serial.println ("Moter one triggered!");
}
else if (ch == 'z') { // If an 's' is received then stop the motor
dc1.setSpeed (0);
dc1.run(RELEASE); // turn it off

 "if the first char is a then set the value[a] to 222"

If you subtract 'a' from the label, you'll get a simple index zero to twenty five.