double int 类型的区别

内部组织格式不同：

po [NSString stringWithFormat:@"%d", f]

107886912

(lldb) po [NSString stringWithFormat:@"%f", f]

976.000000

(lldb) po [NSString stringWithFormat:@"%lld", f]

4402854208

(lldb) p f

(double) $3 = 976