pow log 与 (int)

1.不能用%d输出double类型的数

     double a1=5.3;
     double a2=1234.1234;
     double a3=3412341.12341234;

     double b1=1.5;
     double b2=123.5;
     double b3=23412.5;

     double c1=10.7;
     double c2=2.9;
     double c3=3241324.56251;
     printf("%d\n",a1);
     printf("%d\n",a2);
     printf("%d\n",a3);

     printf("%d\n",b1);
     printf("%d\n",b2);
     printf("%d\n",b3);

     printf("%d\n",c1);
     printf("%d\n",c2);
     printf("%d\n",c3);

输出的值不会变

2.

float pow(float x, float y)

x,y可以为整形，因为进行时会自动转换类型，

但是用%d输出double类型的数则不行。

可以使用(int)。

     cout<<pow(,)<<endl;
     cout<<pow(,)<<endl;
     cout<<pow(,)<<endl;

     printf("\n");

     printf("%f\n",pow(,));
     printf("%f\n",pow(,));
     printf("%f\n",pow(,));

     printf("\n");

     printf("%d\n",pow(,));
     printf("%d\n",pow(,));
     printf("%d\n",pow(,));

     printf("\n");

     printf("%d\n",(int)pow(,));
     printf("%d\n",(int)pow(,));
     printf("%d\n",(int)pow(,));

3.

float log(float x)

(int)使用在在(int)右边的第一个整数。

所以不能使用(int)log(s)/log(2)，而是(int)(log(s)/log(2))。

而求log(2^k)/log(2)时，出现问题，因为是精度不准的问题，如结果为1.99..9xxxd，用(int)后结果为1。

可以采用log(2^k+minv)/log(2)解决，minv=1e-12(或其它)。

     printf("%.15f\n",log()/log());
     printf("%.15f\n",log()/log());
     printf("%.15f\n",log()/log());
     printf("%.15f\n",log()/log());
     printf("%.15f\n",log()/log());

     printf("\n");

     printf("%f\n",(int)log()/log());
     printf("%f\n",(int)log()/log());
     printf("%f\n",(int)log()/log());
     printf("%f\n",(int)log()/log());
     printf("%f\n",(int)log()/log());

     printf("\n");

     printf("%d\n",(int)(log()/log()));
     printf("%d\n",(int)(log()/log()));
     printf("%d\n",(int)(log()/log()));
     printf("%d\n",(int)(log()/log()));
     printf("%d\n",(int)(log()/log()));
     printf("%d\n",(int)(log()/log()));
     printf("%d\n",(int)(log()/log()));

     printf("\n");

     printf("%d\n",(int)(log(+minv)/log()));
     printf("%d\n",(int)(log(+minv)/log()));
     printf("%d\n",(int)(log(+minv)/log()));
     printf("%d\n",(int)(log(+minv)/log()));
     printf("%d\n",(int)(log(+minv)/log()));
     printf("%d\n",(int)(log(+minv)/log()));
     printf("%d\n",(int)(log(+minv)/log()));