Basic knowledge of C language

1、 Carry counting system

1. Decimal system （Decimal）： from 0~9 Ten figures make up , Sew decimal one .
2. Binary system （Binary）： from 0、1 Two numbers make up , Sewing two into one .
3. octal （Octal）： from 0~7 Eight figures make up , Sewing eight into one .
4. Hexadecimal （Hexadecimal）： from 0~9 Ten numbers and A、B、C、D、E、F（ Or lowercase letters ） Six letters , Sew sixteen in one .

2、 Hexadecimal footmark

1. Binary system ：B
2. octal ：Q
3. Decimal system ：D（ If there is no footmark, the default is decimal ）
4. Hexadecimal ： H

3、 The representation of characters inside a computer

• character Inside the computer with ASCII To said .
• ASCII code ： American information interchange code , use low 7 position Binary code （0000000B ~ 1111111B）,ASCII The range of yards is 0 ~ 127, common 128 individual .
• Capital ： A ~ Z(65 ~ 90)
• Lowercase letters ： a ~ z (97 ~ 122)
• Numbers ： 0 ~ 9 （48 ~ 57）
• Space （space）：32
• The characters occupy A byte , Chinese characters account for Two bytes