2-1 Note:
1. C++ only specifies the minimum size of each type of memory, and the number of bytes is at least long long >=long>=int>=short;
2. The character type is divided into char, signed char and unsigned char. The type char will actually appear as which of the above types, which is determined by the compiler; in VS2013, char == signed char;
suggestion:
1. When it is clearly known that the value cannot be negative, use the unsigned type;
2. char is only used to store characters, a small integer is required, signed char or unsinged char (clearly pointed out);
3. Use double for floating-point numbers (double uses 2 words (64 bits) to represent the precision);
2-2 Note:
1、非bool->bool，0->false , 非0->true；
2、bool->非bool，false->0,true->1;
3. When an unsigned type is assigned a value that exceeds the range it represents, the result is the remainder after the initial value is modulo the total number of values represented by the unsigned type;
unsigned char = -1; (0~255);
Actually -1%256 = 255; the remainder after modulo! https://blog.csdn.net/kkkkkkkkq/article/details/72235878
4. When we assign a value to a signed type that exceeds the range it represents, the result is undefined!
signed char c2 = 256; //Assuming char occupies 8 bits, the value of c2 is undefined.