Data commit

Task/Nth-root/C/nth-root.c

@@ -0,0 +1,34 @@
+#include <stdio.h>
+#include <float.h>
+
+double pow_ (double x, int e) {
+    int i;
+    double r = 1;
+    for (i = 0; i < e; i++) {
+        r *= x;
+    }
+    return r;
+}
+
+double root (int n, double x) {
+    double d, r = 1;
+    if (!x) {
+        return 0;
+    }
+    if (n < 1 || (x < 0 && !(n&1))) {
+        return 0.0 / 0.0; /* NaN */
+    }
+    do {
+        d = (x / pow_(r, n - 1) - r) / n;
+        r += d;
+    }
+    while (d >= DBL_EPSILON * 10 || d <= -DBL_EPSILON * 10);
+    return r;
+}
+
+int main () {
+    int n = 15;
+    double x = pow_(-3.14159, 15);
+    printf("root(%d, %g) = %g\n", n, x, root(n, x));
+    return 0;
+}