Square Root

sqrt.c

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

#define PRECISION 0.00001f

double SQRT (double input);
double SQRT_PREC (const double *input, double precision);

int main (int argc, char **argv) {
    double value;
    int cvalue;
    while (1) {
        cvalue = 0;
        printf("Input value to calculate square root:\n");
        scanf("%lf", &value);
        printf("Square root of %lf is %lf\n", value, SQRT(value));
        printf("Do you want to try another value? [Y / N] ");
        while (cvalue != 89 && cvalue != 78 &&
               cvalue != 121 && cvalue != 110) {
            getchar();
            cvalue = getchar();
        }
        if (cvalue == 78 || cvalue == 110) break;
    }
    return 0;
}

double SQRT (double input) {
    return SQRT_PREC(&input, PRECISION);
}

double SQRT_PREC (const double *input, double precision) {
    double greater, middle, lower, test;
    greater = *input;
    lower = greater / 2;
    middle = (lower + greater) / 2;
    test = middle * middle;
    while (fabs(*input - test) >= precision) {
        if (test > *input) {
            greater = middle;
            lower = greater / 2;
        } else {
            lower = middle;
        }
        middle = (lower + greater) / 2;
        test = middle * middle;
    }
    return middle;
}