Speed up a square root c++ prog

[Craig McRae]

Hello All, Could you help me speed up a program? It's designed to find the square root of a number.

#include

using namespace std;

int main()
{
float a;
float c;
cout << "Square root calculator!" << endl;
cout << "Enter the number you want to square root" << endl;
cin >> a;
cout << "Enter an educated guess" << endl;
cin >> c;
cout << "The squareroot of " << a << " is: " << endl;
do
c = (c + (a/c))/2;

while ( c != a/c );

{ cout << c << endl;
} 

return 0;
}

My problem is that it get remarkably slow around 55ish. Any advice it appreciated

[Richard Andrew x64]

I can see where it would come to a dead stop:

while ( c != a/c );

The difficult we do right away... ...the impossible takes slightly longer.

[Chris Losinger]

c = sqrt(a);

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[jeron1]

I'm guessing your issue is the while(). Comparing two floats can be tricky.

while ( c != a/c );

this[^] link may help.

[leon de boer]

That is the problem with the Babylonian method you have used. Paul Hsieh has a very good webpage on everything about square roots but were afraid to ask. http://www.azillionmonkeys.com/qed/sqroot.html[^] It includes details most of the techniques from the standard C library, to the faster integers version that NVidia and Quake use.