Here is the example program that computed square roots without using the predefined sqrt function:
1 int main()
2 {
3
4 double x, y;
5 cout << "Enter a positive number: ";
6 cin >> x;
7
8 y = ( 1.0 + x ) /2;
9
10 while( fabs(x - y * y) > 0.0001 ) {
11 y = (y + x/y)/2;
12 }
13 cout.setf(ios::fixed);
14 cout.precision(4);
15
16 cout << "x = " << x << endl;
17 cout << "y = " << y << endl;
18 cout << "y*y = " << y * y << endl;
19
20 return 0;
21 }