Added 3 out of 4 integral functions to ass5.

modsim/ass2/func_ptr.h

-typedef double (*func_ptr)(double x);
+typedef double (*func_ptr)(double);

modsim/ass2/q5.c

 #include <stdlib.h>
 #include <stdio.h>
 #include <math.h>
+#include "func_ptr.h"
 
-int main(void) {
+#define DX 1e-6
+
+typedef double (*method_ptr)(func_ptr, double, double);
+
+double rectangle(func_ptr f, double a, double b) {
+    return (b - a) * f((a + b) / 2);
+}
+
+double trapezoidal(func_ptr f, double a, double b) {
+    return 0.5 * (b - a) * (f(a) + f(b));
+}
+
+double simpson(func_ptr f, double a, double b) {
+    return (2 * rectangle(f, a, b) + trapezoidal(f, a, b)) / 3;
+}
+
+double integral(func_ptr f, method_ptr method, double a, double b) {
+    int steps = (int)((b - a) / DX), i;
+    double x, surface = 0;
 
+    for( i = 0; i < steps; i++)
+        surface += method(f, x = a + i * DX, x + DX);
+
+    return surface;
+}
+
+double f1(double x) {
+    return pow(M_E, -x);
+}
+
+double f2(double x) {
+    return x * pow(M_E, -x);
+}
+
+#define PRINT_INTEGRAL(func, method, a, b) (printf(#func " from " #a " to " \
+    #b " using " #method " method: %.11f\n", integral(&func, &method, a, b)))
+
+int main(void) {
+    PRINT_INTEGRAL(f1, rectangle, 0, 1);
+    PRINT_INTEGRAL(f1, trapezoidal, 0, 1);
+    PRINT_INTEGRAL(f1, simpson, 0, 1);
 
     return 0;
 }