C code not running as expected

Question

I wrote a simple c program to find square roots of 2,3,4,5 using newton-raphson iteration technique. This code runs to find and display square root of 2 only. Afterwards it hangs. I could not figure out the problem with this code:

# include<stdio.h>

    float square(float x);
    float absolutevalue(float x);

int main(void)
{
    printf("square root of 2 is %f\n", square(2));
    printf("square root of 3 is %f\n", square(3));
    printf("square root of 4 is %f\n", square(4));
    printf("square root of 5 is %f\n", square(5));

    return 0;
}

float square(float x)
{
    float epsilon = 0.0000001;
    float guess = 1;

    while (absolutevalue(guess*guess - x) >= epsilon)
        guess = ((x/guess) + guess) / 2;

    return guess;
}

float absolutevalue(float x)
{
    if (x < 0)
        x = -x;

    return x;
}

`square` is a reserved identifier when used with external linkage — ouah, Dec 21 '12 at 12:50
Your epsilon is too small, the float type doesn't have enough significant digits. Replace all float by *double* for a quick fix. — Hans Passant, Dec 21 '12 at 12:50
Looking at the [output here](http://stacked-crooked.com/view?id=a9548fc448972258896a9e17cb43e8a5), printing the value of `guess` in the loop, you can see the problem quite easily. — Tony The Lion, Dec 21 '12 at 12:54
@Hans Passant increasing the size of epsilon worked.. yet it is not clear to me why it was hanging earlier? could you explain a bit more? — user1825355, Dec 21 '12 at 12:56
probably because you entered a land known as Undefined Behavior — Tony The Lion, Dec 21 '12 at 12:57
@user1825355 - Check here: http://stackoverflow.com/questions/2386772/difference-between-float-and-double — Mike, Dec 21 '12 at 13:03
SO is not for code review, so your question (what question) is not really appropriate, here. — Jens Gustedt, Dec 21 '12 at 13:04
@JensGustedt: The OP asked a specific question, namely why the code was hanging right after seeing the square root of 2. — RonaldBarzell, Dec 21 '12 at 13:33

score 1 · Accepted Answer · answered Dec 21 '12 at 14:23

1

Everything will work fine if you replace float with double everywhere.

answered Dec 21 '12 at 14:23

piokuc

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C code not running as expected

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