This is a simple project in pure C that I did for a classmate's homework while I was in college.
A calculator program support simple math expression calculation and variable declaration.
for example
int a, b, c;
float d, e;
a = 5;
b = 7;
c = ( 12 + 23 ) / ( a + 12 ) * ( b + 8 );
d = c + 1.2 + sin 45;
e = d + b * 5.6;