Merge pull request #456 from Gorzoid/monte_carlo_c_fix

Monte carlo C fix

Author: Gathros

contents/monte_carlo_integration/code/c/monte_carlo.c

@@ -8,29 +8,29 @@ bool in_circle(double x, double y, double radius) {
     return x * x + y * y < radius * radius;
 }
 
-void monte_carlo(int samples) {
+double monte_carlo(int samples) {
     double radius = 1.0;
     int count = 0;
 
     for (int i = 0; i < samples; ++i) {
-        double x = (double)rand() * 2.0 / RAND_MAX - 1.0;
-        double y = (double)rand() * 2.0 / RAND_MAX - 1.0;
+        double x = (double)rand() * radius / RAND_MAX;
+        double y = (double)rand() * radius / RAND_MAX;
 
         if (in_circle(x, y, radius)) {
             count += 1;
         }
     }
 
-    double estimate = 4.0 * count / (samples * radius * radius);
-
-    printf("The estimate of pi is %f\n", estimate);
-    printf("Percentage error: %0.2f%\n", 100 * fabs(M_PI - estimate) / M_PI);
+    return 4.0 * count / samples;
 }
 
 int main() {
     srand(time(NULL));
 
-    monte_carlo(1000000);
-
+    double estimate = monte_carlo(1000000);
+	
+    printf("The estimate of pi is %f\n", estimate);
+    printf("Percentage error: %0.2f%\n", 100 * fabs(M_PI - estimate) / M_PI);
+	
     return 0;
 }