Update C implementations for Verlet algorithms

contents/verlet_integration/code/c/verlet.c

@@ -1,55 +1,61 @@
 #include <stdio.h>
 
-void verlet(double pos, double acc, double dt) {
-    double prev_pos, temp_pos, time;
+void verlet(double *time, double pos, double acc, double dt) {
+    double prev_pos, temp_pos;
     prev_pos = pos;
-    time = 0;
+    *time = 0.0;
 
     while (pos > 0) {
-        time += dt;
+        *time += dt;
         temp_pos = pos;
         pos = pos * 2 - prev_pos + acc * dt * dt;
         prev_pos = temp_pos;
     }
-
-   printf("%f\n", time);
 }
 
-void stormer_verlet(double pos, double acc, double dt) {
-    double prev_pos, temp_pos, time, vel;
+void stormer_verlet(double *time, double *vel,
+                    double pos, double acc, double dt) {
+    double prev_pos, temp_pos;
     prev_pos = pos;
-    vel = 0;
-    time = 0;
+    *vel = 0.0;
+    *time = 0.0;
+
     while (pos > 0) {
-        time += dt;
+        *time += dt;
         temp_pos = pos;
         pos = pos * 2 - prev_pos + acc * dt * dt;
         prev_pos = temp_pos;
 
-        vel += acc * dt;
+        *vel += acc * dt;
     }
-
-   printf("%f\n", time);
 }
 
-void velocity_verlet(double pos, double acc, double dt) {
-    double time, vel;
-    vel = 0;
-    time = 0;
+void velocity_verlet(double *time, double *vel,
+                     double pos, double acc, double dt) {
+    *vel = 0.0;
+    *time = 0.0;
+
     while (pos > 0) {
-        time += dt;
-        pos += vel * dt + 0.5 * acc * dt * dt;
-        vel += acc * dt;
+        *time += dt;
+        pos += (*vel) * dt + 0.5 * acc * dt * dt;
+        *vel += acc * dt;
     }
-
-   printf("%f\n", time);
 }
 
 int main() {
-    verlet(5.0, -10, 0.01);
-    stormer_verlet(5.0, -10, 0.01);
-    velocity_verlet(5.0, -10, 0.01);
+    double time, vel;
+
+    verlet(&time, 5.0, -10, 0.01);
+    printf("Time for Verlet integration is: %lf\n",
+           time);
+
+    stormer_verlet(&time, &vel, 5.0, -10, 0.01);
+    printf("Time and velocity for Stormer Verlet integration is: %lf, %lf\n",
+           time, vel);
+
+    velocity_verlet(&time, &vel, 5.0, -10, 0.01);
+    printf("Time and velocity for velocity Verlet integration is: %lf, %lf\n",
+           time, vel);
 
     return 0;
 }
-

contents/verlet_integration/verlet_integration.md

@@ -35,7 +35,7 @@ Here is what it looks like in code:
 {% sample lang="cpp" %}
 [import:4-17, lang:"c_cpp"](code/c++/verlet.cpp)
 {% sample lang="c" %}
-[import:3-16, lang:"c_cpp"](code/c/verlet.c)
+[import:3-14, lang:"c_cpp"](code/c/verlet.c)
 {% sample lang="java" %}
 [import:2-18, lang:"java"](code/java/verlet.java)
 {% sample lang="py" %}
@@ -81,7 +81,7 @@ Here's what it looks like in code:
 {% sample lang="cpp" %}
 [import:20-36, lang:"c_cpp"](code/c++/verlet.cpp)
 {% sample lang="c" %}
-[import:18-33, lang:"c_cpp"](code/c/verlet.c)
+[import:16-31, lang:"c_cpp"](code/c/verlet.c)
 {% sample lang="java" %}
 [import:21-40, lang:"java"](code/java/verlet.java)
 {% sample lang="py" %}
@@ -138,7 +138,7 @@ Here is the velocity Verlet method in code:
 {% sample lang="cpp" %}
 [import:38-49, lang:"c_cpp"](code/c++/verlet.cpp)
 {% sample lang="c" %}
-[import:35-46, lang:"c_cpp"](code/c/verlet.c)
+[import:33-43, lang:"c_cpp"](code/c/verlet.c)
 {% sample lang="java" %}
 [import:43-57, lang:"java"](code/java/verlet.java)
 {% sample lang="py" %}
@@ -223,4 +223,3 @@ $$
 \newcommand{\bfomega}{\boldsymbol{\omega}}
 \newcommand{\bftau}{\boldsymbol{\tau}}
 $$
-