CODEWITHSUNDEEP
c
CUcainiao
CUcainiao

Reputation: 1

a few bugs while executing the program

I want to write a program to see if an integer is the power of another integer(true return 1 and false return 0). And the code is as follows:

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

int cal_base_power(int);

int main()
{
int x,r;
printf("Please input an integer\n");
scanf("%d\n",&x);
r=cal_base_power(x);
printf("result is %d\n",r);
}

int cal_base_power(int input)
{
int i=2;
double a=pow(input,(double)1/i);
while (a>=2)
{
        if ((double)a==(int)a)

        return 1;               

        i++;
        a=pow(input,(double)1/i);

}

    return 0;


}

It is ok with 4,8,125 some cases like these. But failed when input 216 and 343. Also it will not automatically output 0 and 1. I must input some random characteristics before the result 0 or 1 comes out. Can anyone help me? I know it is quite easy. But I really need your help

Upvotes: 0

Views: 90

Answers (1)

Mysticial
Mysticial

Reputation: 471379

You can't do equality comparisons on floating-point.

(double)a==(int)a

Due to round-off error, a might not be exactly an integer even though it's supposed to be.

EDIT:

There's two ways to do this:

  1. Allow tolerance on the comparison: fabs(a - (int)a) < 0.0001 (or something like that, you'll need to tweak the threshold.)
  2. Round a to the nearest integer and power it back up (using integers only) to see if it matches the input.

Upvotes: 4

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