Why is this program for converting cartesian coordinates to Polar coordinates is not giving correct omega value?

Question

This is my program in C:

  #include<stdio.h>
  #include<math.h>
  int main()
  {   int x, y;
    printf("Enter the cartesian coordinates to be converted into respective polar coordinates");
    scanf(" %d %d", &x, &y );
    float r = sqrt(pow(x,2) + pow(y,2));
    float omega = atan(y/x);
    printf("The required polar coordinates are: (%f, %f)", r, omega);
    return 0;
}

Following input is made:

5 12

And I get:

The required polar coordinates are: (13.000000, 1.107149)

I think the output is only half correct.

I expected, if unit is radian, the output must be:

The required polar coordinates are: (13.000000, 0.3944444)

But the output comes out to be:

The required polar coordinates are: (13.000000, 1.107149)