Problems of float or double calculations being not quite exact.

[Guest_imported]

Hi, I am trying to write a program that works out pythagoreon triples. Could someone help me so that the calculations give the correct answer?


#include <stdio.h>
#include <math.h>
#define N 20

int main(void) {
int i,j,intsum; float sum;
for (i=1; i <=N; ++i) {
for (j=1; j <= N; ++j) {
sum = sqrt(i*i + j*j);
intsum = sum; /* integer part of sum only */
/* if no fractional part, then perfect square*/

if ( (sum - intsum) == 0)
if (i<j)
if (intsum % 2 !=0)
printf(&quot;%d %d %d\n&quot;, i, j, intsum);

}
}
return 0;
}

 

[Lim]

Looks fine.

May be some platforms have problem with:
float sum; Try it make double sum;
Also intsum = (int)sum;
and most important:
if ((sum - (double)intsum) == 0.)

If it will not help post yours output.

 

[migur]

Guys,
you can not say
if(sum - (double)intsum == 0.0) no no!

double delta = 0.005; // use your value here
then always compare those two with your delta!
x - y < delta in this fashion.

Don't forget that float or double keeps approximation to the real value, for example float x=1.0; could be 0.999999 in fact

 

[Leibnitz]

#include <stdio.h>
#include <math.h>
#define N 20

int main(void) {
int i,j,intsum; float sum;
for (i=1; i <=N; ++i) {
for (j=1; j <= N; ++j) {
sum = (float)sqrt(i*i + j*j);
intsum = (int)sum; /* integer part of sum only */
/* if no fractional part, then perfect square*/

if ( (sum - intsum) == 0)
if (i<j)
if (intsum % 2 !=0)
printf(&quot;%d %d %d\n&quot;, i, j, intsum);

}
}
return 0;
}

Now it will compile without any warnings.