// define global variables
float ao = 0;
float bo = 0;

int mand(float x, y){ //user-defined function
    int a = x/2; 
    int b = y/3;
    int i = a+b;
    ao = a; // pass values a to global variable ao
    bo = b; // pass values b to global variable bo
    return(i);
}

v@Cd = set(ao, bo, mand(1, 0.3)); // use variables ao and bao in main program, as well as i, for example in color attribute

// define global variables
float ao = 0;
float bo = 0;


int mand(float x, y, ao, bo){ //user-defined function
    int a = int(x/2); 
    int b = int(y/3);
    int i = a+b;
    ao = a; // pass values a to global variable ao
    bo = b; // pass values b to global variable bo
    return(i);
}

v@Cd = set(ao, bo, mand(1.0, 0.3, ao, bo)); // use variables ao and bao in main program, as well as i, for example in color attribute

#define MY_INT            123
#define otherInt          999

int foo( float ax; ) {
    int val = (ax > 0) ? MY_INT : otherInt;
    return(val);
}

i@a = foo(@P.x);

... 
int a = int(x/2.0); 
int b = int(y/3.0);
...