十进制转二进制
方法：短除法，立向取值
例子：
2|90··············································0--------↑
2|45··············································1--------↑
2|22··············································0--------↑
2|11··············································1--------↑
2|5··············································1--------↑
2|2··············································0--------↑
1--------------------------------------------------------↑
(90)10=(1011010)2
二进制转十进制
方法：取第n位的2的n-1次方，算出所有的后相加
例子：
(1011010)2=1*2^6+0*2^51*2^4+1*2^3+0*2^2+1*2^1+0*2^0=64+16+8+2=(90)10
(1001010)2=1*2^6+0*2^5+0*2^4+1*2^3+0*2^2+1*2^1+0*2^0=64+8+2=(74)10