How declare the @ at sign dollar at C++?

For example if the charc enter abc@my.com

once the use enter @ then should return different case! But how to declare @ in the C++?

case q3: switch(y){ case '@': return q4; default: return q0; } case q4: switch(y){ case 'a': case 'b': case 'c': case 'd': case 'e': case 'f': case 'g': case 'h': case 'i': case 'j': case 'k': case 'l': case 'm': case 'n': case 'o': case 'p': case 'q': case 'r': case 's': case 't': case 'u': case 'v': case 'w': case 'x': case 'y': case 'z': return q5; default: return q0;