Clock Coordinates - c

Question

I am new to c programming and I had received an assignment not too long ago and ended up doing good enough (points were taken off for not using a for loop). Here is what is from my assignment. "Write a program that prompts the user for the radius of an analog clock, and then prints the x and y coordinates of the 12 hour marks for that clock.You may assume that the origin for the x and y axes is in the center of the clock"
I was confused on how to use the for loop because I was trying to figure out a way how. I know it easy but I struggle with little things. This ended up to copy-pasting code, which led to massive amounts of code. I was wondering if I can get any hints on how to do this program with a for loop rather than having to write all this code Here is my code, but I will not display all of it because there is not point. (Also wondering if I do need arrays? Let me know that too, sorry for the weird format, I have not figured out how to make the code blend in).
int main () {
float x [12];
float y [12];
float rad;
int i, theta = 0;
printf("Enter the radius of the clock\n");
scanf("%f", &rad);
x[0] = rad * cos(90*M_PI/180);
y[0] = rad * sin(90*M_PI/180);
x[1] = rad * cos(60*M_PI/180);
y[1] = rad * sin (60*M_PI/180);
x[2] = rad * cos (30*M_PI/180);
y[2] = rad * sin (30*M_PI/180);
x[3] = rad * cos (0 * M_PI/180);
y[3] = rad * sin (0* M_PI/180);
x[4]= rad * cos (330*M_PI/180);
y[4]= rad * sin (330*M_PI/180);
x[5] = rad * cos (300*M_PI/180);
y[5] = rad * sin (300*M_PI/180);
x[6] = rad * cos (270*M_PI/180);
y[6] = rad * sin (270*M_PI/180);
x[7] = rad * cos (240*M_PI/180);
y[7] = rad * sin (240*M_PI/180);
x[8] = rad * cos (210*M_PI/180);
y[8] = rad * sin (210*M_PI/180);
x[9] = rad * cos (180*M_PI/180);
y[9] = rad * sin (180*M_PI/180);
x[10] = rad * cos (150*M_PI/180);
y[10] = rad * sin (150*M_PI/180);
x[11] = rad * cos (120*M_PI/180);
y[11] = rad * sin (120*M_PI/180);
printf("The x and y coordinates of the 12 o'clock mark are (%f , %f)\n", x[0], y[0]);
I use printf statement for all 12 arrays.
The output is suppose to look like this "The x and y coordinates of the 12 o'clock mark are (0.000000 , 1.000000) and it changes depending on the radius." Thank you!

Answer 1

Just taking sequential statements like this and abstracting them into a loop is a task that requires factoring out the parts that are common.
Start with these two pairs of statements:
x[0] = rad * cos(90*M_PI/180);
y[0] = rad * sin(90*M_PI/180);
x[1] = rad * cos(60*M_PI/180);
y[1] = rad * sin (60*M_PI/180);
What changes here, between the first pair and the second? Only the index of x/y and the input angle.
We can see from scanning the rest of the statements that the index increments sequentially (value increases by one) with each subsequent pair. So we could use a simple loop index as the array indices:
for (int i = 0 ; i < 12; i++) {
x[i] = rad * cos(90*M_PI/180);
y[i] = rad * sin(90*M_PI/180);
}
Okay, good start, but now all 12 values will use 90 degrees. How can we abstract out the angle to make our loop work equivalent to the statements you used? Start by deciding what the increment should be -- in this case, it's not just by 1 like i was. We want 30 degrees, which is also one twelfth of 360.
const size_t divisions = 12;
const size_t degrees_per_iter = 360 / divisions;
for (int i = 0 ; i < divisions; i++) {
x[i] = rad * cos(i*degrees_per_iter*M_PI/180);
y[i] = rad * sin(i*degrees_per_iter*M_PI/180);
}
Now, we're off to a good start. We will cover all 12 values of x and y this way. But we're not 100% identical to the original code. Is the order critical? Let's assume that it is critical, and that will raise the bar a bit.
In order to stay within the valid degree range and keep the output function continuous, we need to use modulus or remainder division.
const size_t divisions = 12;
const size_t degrees_per_iter = 360 / divisions;
const size_t start_angle_deg = 90;
for (int i = 0 ; i < divisions; i++) {
const size_t angle_deg = (start_angle_deg + (i * degrees_per_iter)) % 360;
const float x = rad * cos(angle_deg * M_PI/180);
const float y = rad * sin(angle_deg * M_PI/180);
printf("The x and y coordinates of the 12 o'clock mark are (%f , %f)\n", x, y);
}
Also wondering if I do need arrays
Yes, indeed you do! But you were already using them for x and y. No further arrays are necessary. No arrays are necessary.

Answer 2

I would not have used arrays, I would've done something more like this:
int dir = 0;
char hour = 3;
for(int i=0; i<12; i++){
float xcoord = rad * cos(dir*M_PI/180);
float ycoord = rad * sin(dir*M_PI/180);
printf(...);
dir += 30;
hour++;
hour = (hour > 12) ? 1 : hour+1;
}