CODEWITHSUNDEEP
c
Kurt Peek
Kurt Peek

Reputation: 57611

C code with several conditional statements giving an unexpected result

I'm trying to adapt a C program on reinforcement learning, https://webdocs.cs.ualberta.ca/~sutton/book/code/pole.c, to Python to participate in the OpenAI Gym. I've copied the get_box function into a separate test program:

#include <stdio.h>

int get_box(float x, float x_dot, float theta, float theta_dot);

int main() {

    int box;
    box = get_box(0.01, 0.01, 0.01, 0.01);

    printf("The value of box is : %x\n", box);

    return 0;
}

#define one_degree 0.0174532    /* 2pi/360 */
#define six_degrees 0.1047192
#define twelve_degrees 0.2094384
#define fifty_degrees 0.87266

int get_box(x,x_dot,theta,theta_dot)
float x,x_dot,theta,theta_dot;
{
  int box=0;

  if (x < -2.4 ||
      x > 2.4  ||
      theta < -twelve_degrees ||
      theta > twelve_degrees)          return(-1); /* to signal failure */

  if (x < -0.8)                box = 0;
  else if (x < 0.8)                box = 1;
  else                             box = 2;

  if (x_dot < -0.5)                ;
  else if (x_dot < 0.5)                box += 3;
  else                         box += 6;

  if (theta < -six_degrees)            ;
  else if (theta < -one_degree)        box += 9;
  else if (theta < 0)              box += 18;
  else if (theta < one_degree)         box += 27;
  else if (theta < six_degrees)        box += 36;
  else                         box += 45;

  if (theta_dot < -fifty_degrees)   ;
  else if (theta_dot < fifty_degrees)  box += 54;
  else                                 box += 108;

  return(box);
}

which I call scratch.c. If I compile this program with gcc scratch.c -lm and run it with ./a.out, I get the following printed output:

The value of box is : 55

However, if I go through the conditional statements manually I would expect to get 1 + 3 + 27 + 54 = 85, which is also what I get with my Python program. Why does the program print 55?

Upvotes: 0

Views: 73

Answers (2)

Tarun Singh
Tarun Singh

Reputation: 64

Because your output getting converted to hexadecimal number. If you convert 55 to decimal, then it is equivalent of 85.

Upvotes: -1

Ronald
Ronald

Reputation: 2882

If you'd do a printf("%d\n", box) instead of printf("%x\n", box) you'll get the decimal value printed. 0x55 = 5*16 + 5 = 85

Upvotes: 3

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