只要加一個基準值 將相差小於基準值的兩數視做相同

#include <stdio.h>
const double capaity = 1e-6; //可以更小 1e-12;
// (99999 - 100000) / 100000 = -1e-5;

int main()
{
 int goods, val, valn;
 scanf("%d", &goods);
 while (goods--)
 {
    scanf("%d%d", &val, &valn);
    double rat = (double)(valn - val) / val * 100;
    if(rat >= 0.0)printf("%.2lf%% ",rat+capaity);
    else printf("%.2lf%% ",rat-capaity);
    if (rat >= 10.0 || rat <= -7.0) printf("dispose\n");
    else printf("keep\n");
 }
 return 0;
}