Some math related code for calculatin binomial coef, nth-fibonacci and sin

sin.c

@@ -0,0 +1,36 @@
+#include <stdio.h>
+
+#define HALFPI 1.5707963268
+
+// Compute factorial iteratively
+double factorial(int n) {
+    double result = 1.0;
+    for (int i = 2; i <= n; ++i) {
+        result *= i;
+    }
+    return result;
+}
+
+double abs_double(double x) { return x < 0 ? -x : x; }
+
+// SICP-style iterative approximation for sin(x)
+double sin_iter(double x) {
+    double term = x;   // First term of the series
+    double sum = term; // Initial sum
+    // double prev_sum;
+    int n = 1; // Starting from x^3/3!
+
+    do {
+        // prev_sum = sum;
+        term *= -x * x / ((2 * n) * (2 * n + 1)); // Next term in series
+        sum += term;
+        ++n;
+    } while (abs_double(term) > 1e-10); // Stop when term is sufficiently small
+
+    return sum;
+}
+
+int main() {
+    printf("Approximated sin(pi/2) = %.10f\n", sin_iter(HALFPI));
+    return 0;
+}