mirror of https://github.com/TheAlgorithms/C
124 lines
2.6 KiB
C
124 lines
2.6 KiB
C
/**
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* @file
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* @brief Function to convert a Cartesian co-ordinate to polar form.
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*/
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#define _USE_MATH_DEFINES /**< required for MS Visual C */
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#include <assert.h>
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#include <math.h>
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#include <stdio.h>
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#include <stdlib.h>
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/**
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* @brief Function to convert cartesian coordinates to polar.
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*\f{eqnarray*}{
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r &=& \sqrt{x^2+y^2}\\
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\theta &=& \atan\frac{y}{x}
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\f}
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* @param [in] x absicca value
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* @param [in] y ordinate value
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* @param [out] r pointer to store polar radius
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* @param [out] theta pointer to store polar angle (in radian)
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*/
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void to_polar(double x, double y, double *r, double *theta)
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{
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double thetaFinal = 0.f;
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*r = sqrt(x * x + y * y);
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if (x != 0)
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{
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if (y != 0)
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{
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*theta = atan(y / x);
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if ((x > 0 && y > 0) || (x == -y))
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{ // Q1
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thetaFinal = *theta;
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}
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else if (x < 0 && y > 0)
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{ // Q2
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thetaFinal = *theta + M_PI;
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}
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else if (x < 0 && y < 0)
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{ // Q3
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thetaFinal = *theta - M_PI;
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}
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else if (x > 0 && y < 0)
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{ // Q4
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thetaFinal = 2 * M_PI - *theta;
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}
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else
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{
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fprintf(stderr, "Should not reach here!\n");
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}
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}
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}
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else
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{ // exceptions when no actual angle is present
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if (y > 0)
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{
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thetaFinal = M_PI / 2;
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}
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else
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{
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thetaFinal = -(M_PI / 2);
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}
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}
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if (y == 0)
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{
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if (x > 0)
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{
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thetaFinal = 0;
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}
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else
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{
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thetaFinal = -M_PI;
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}
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}
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*theta = thetaFinal;
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}
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/**
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* @brief Generate a random number in the given limits
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*
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* @param lim1 lower limit
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* @param lim2 upper limit
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* @return random number in the given range
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*/
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double get_rand(double lim1, double lim2)
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{
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double r = (double)rand() / RAND_MAX; // value in [0,1)
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return (lim2 - lim1) * r + lim1; // scale to range
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}
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/**
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* @brief Test implementation
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*
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*/
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void test()
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{
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srand(10);
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int NUM_TESTS = 5;
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for (int i = 0; i < NUM_TESTS; i++)
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{
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double r, theta;
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printf("Test %d.... ", i);
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double x = get_rand(-5, 5);
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double y = get_rand(-5, 5);
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printf("(%.2g, %.2g).... ", x, y);
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to_polar(x, y, &r, &theta);
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assert(fabs(r - hypot(x, y)) < 0.01);
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assert(fabs(theta - atan2(y, x)) < 0.01);
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printf("passed\n");
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}
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}
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/** Main function */
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int main()
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{
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test();
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return 0;
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}
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