recursive problem

Posted on 2008-10-05
Last Modified: 2012-05-05
I have a recursive program that is suppose to return the square root of a number recursivley, the program will run, but it returns 1. please help
#include <stdio.h>

double square_root(double low, double high);

int main(void)


    float number;

    double root;


    printf("Enter a number to compute the square root of.\n");

    scanf("%f", &number);


    root = square_root(1, number);


    printf("The square root of %.3f is about %.3lf\n", number, root);



    return 0;


	double square_root(double low, double high)


    float mid;


    mid = (high + low) / 2;

    //Base Case

    if((mid*mid) == high)

        return mid;

     //Stops when the high and low numbers are within 0.001 of one another.   

    if((high - low) < 0.001)

        return mid;


    if((mid*mid) > high)

        return square_root(low, mid);


    return square_root(mid, high);


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Question by:mikeregas
  • 4
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LVL 84

Expert Comment

ID: 22646982
Are you sure you have the correct recursion?
The method you use looks like it would work better passing 3 numbers.
or else changing

Author Comment

ID: 22647108
I need to take a number say 19.7 and then it is suppose to return 4.438 is the example that I was given. I know that I am suppose to take two number the low which would be 0 and the high and which would be 19.7 and recursively bring it down to an approximate square root. So there would be a third number in the equation the  mid.
LVL 45

Expert Comment

ID: 22647118
>square_root(1, number);
second arg is the number whose sq root you want.

Your recursive calls are
>return square_root(low, mid);<<<------ you are calculating sq root of mid!!
>return square_root(mid, high);


Expert Comment

ID: 22647340
Hello mikergas,

You are using "Babylonian method" to calculate square root. You are not using it in right way.
For proer desciption of babylonian method can be found in link

I am attaching modified and working version of your code..
<code edited out>



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Expert Comment

ID: 22648784
I will take care in future
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Author Comment

ID: 22650155
I am confused on what is right in my code and what is wrong? can you please give me some direction to go in. my code is return a 1 for any number that I input and I know that is worng.
LVL 45

Expert Comment

ID: 22650289
http:#22647118 lists your problem
http:#22646982 hints at a solution

Expert Comment

ID: 22650877
According to algorithm
x(n+1) = 1/2( x(n) + a / x(n) )

where a is the number for which square root should be calculated.
Change calculation of 'mid' to above formula.

Also, since you are always calling function recursively with low as 1, your answer is always converging to 1.


Author Comment

ID: 22651030
x(n+1) = 1/2( x(n) + a / x(n) ) let me make sure that I understand this. if a is the number that I am trying to get the root of then x is a function of what? I am truely lost with recursion

Accepted Solution

lakshmikarle earned 500 total points
ID: 22651108
n can take values like 0,1,2,3
Assume x(0) = 1.
Go thru the link I have posted

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