Negative operator isn't working

All of the following compile to invalid C code.

```
a = -1
b = -1.0
c = 13 + -5
```

Specifically, 

```
a = 1
b = 2
c = a + -b
```

becomes

```
int a;
a = 13; 
int b;
b = 17; 
Integer_assign((c + (a - b)));
```

in which `Integer_assign` is an undefined reference
and `c` is an undeclared identifier

The negative operator should work as it does in C.
