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1sem/programming basics/6/2_100.cpp

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+// pb_6_2_100.cpp
+// Горбацевич Андрей
+#include <iostream>
+#include <cmath>
+using namespace std;
+
+double arctg(double, double);
+double mant(double);
+
+int main() {
+    double x, d;
+    cout << "x, d >>>";
+    cin >> x >> d;
+    if ((x < -1) or (x > 1)) {
+        cout << "err: x not in range";
+        return 0;
+    }
+
+    double oarctg = arctg(x, d);
+    double carctg = atan(x);
+    cout << "  own arctg(x) = " << oarctg << endl;
+    cout << "cmath arctg(x) = " << carctg << endl;
+    cout << "          diff = " << oarctg - carctg << endl;
+}
+
+double arctg(double x, double delta) {
+    double out = x;
+    double px = x;
+    int den = 1;
+    bool neg = false;
+    double pout = out + 0.1f;
+    while (abs(mant(out)-mant(pout)) > delta) {
+        pout = out;
+        neg = !neg;
+        x *= px*px;
+        den += 2;
+        out += x/den * (neg? -1 : 1);
+    }
+    return out;
+}
+
+double mant(double num) {
+    return num - (int)num;
+}