was not declared in this scope

#include <stdio.h>
#include
#include <math.h>

int main (){

char s1, a, b, c;

printf(“Informe a classe do aluno: “);
scanf(”%c”, s1);

if (s1 == a ){
printf (“O aluno esta no 1Y. Que eh a melhor sala.”);

}if (s1 == b ){
printf (“O aluno esta no 1W.”);

}if (s1 == c ){
printf (“O aluno esta no 1X.”);

}else{
printf (“Essa classe nao existe!”);
}
}

I have no idea what is wrong with this code ; -;
Please, help me

I have no idea what is wrong with this code ; -;

lack of code tags.
Not Arduino code.
No stdin for scanf to work.

scanf needs a ptr to variable

scanf("%c", & s1);

what are the values of a, b, c or did you mean 'a', 'b', 'c'? not sure

Oh, and no explanation of what the program is expected to do.