C语言英文课件11：位运算.ppt

11.1 Number Expressed in Computer 1.Bit and Byte Memory in computer system is constituted of many named byte units. One byte is made up of eight bits ,and the value is 0 or 1 of every bit. The bit in the right side is called “the lowest bit”, and its number is 0. The bit in the left side is called “the highest bit”, and set the number to each bit from the lowest to highest in order. Diagram 11-1 is the number of each bit in one byte . Fig 11-1 The number of each bit in one byte 2.Digit Expressed by Initial Code Digit expressed by initial code is that using the highest bit as a sign bit( 0 refers to positive number, 1 refers to negative number), the other bits represent to themselves’ absolute value ( expressed in binary). In order to simple description , we use one byte to express one integral in this class. For example, the initial code of +9 is └→sign bit 0 refers to positive number the initial code of -9 is └→ sign bit 0 refers to negative number 3.Digit Expressed by Opposite Code digit expressed by opposite code includes two circumstances: （1）opposite code of positive number: the same as the initial code. For example, the opposite code of +9 is （2） opposite code of negative number: sign bit is 1, other bits is opposite to their absolute value (1 turns to 0, 0 turns to 1). For example, the opposite code of -9 is: because it is a negative number , sign bit is 1; other seven bits is the opposite of its absolute value that the initial of +9 , so the opposite of -9 is 4. Digit Expressed by Complement Code Digit expressed by complement code also includes two circumstances : （1）the complement code of positive number: the same as the initial code. For example, the complement code of +9 is 0001001. （2）the complement of negative number: sign bit is 1, other bits is opposite to their absolute value’s initial