Of course, expressions can contain variables. With arithmetic expressions, the type of the variable determines what type of operations are performed.
What is displayed by this program:
#include <stdio.h>
/* Puzzle E11 -- variables */
int main()
{
int a = 7;
int d = 3;
printf("Expressions evaluate to: %d and to %f\n", a/d, a/3.0 );
return 0;
}