#include <stdlib.h>
#include <stdio.h>
#include <math.h>

#define PRECISION pow( 10, -6 )

float mysqrt( float, float );

int main( ){
    float x = 0.0;
   
    for( ;; )
    {
        printf( "Enter number: " );
        scanf( "%f", &x );
       
        if( x < 0 ){
            printf( "Number is less than 0, exiting cowardly!\n" );
            exit( 0 );
        }

        printf( "Square root: %f\n", mysqrt( x, PRECISION ) );
    }

}

/**
 * Function for calculating the square root of a given number "r"
 * with a precision of "e" 
 *
 * @param   float   r   number whose root to find
 * @param   float   e   root precision
 *
 * @return  float   the root of r
 */
float mysqrt( float r, float e ){
    float x = r / 2.0, x_last = 0;

    while( fabs( x - x_last ) / x > e ){
        x_last = x;
        x = 0.5 * ( x + r / x );
    }

    return x;
}