C language will automatically convert operand types during operation. The specific strategy is to convert data types that occupy less space into data types that occupy more space. When performing an operation, for example, if the double type is divided by the int type, then the int will be converted to a decimal before performing the operation. If it is the same level, it will not be converted, so the result of b/a is still plastic. The decimal part of the operation result will be automatically cut off, so the result of 3/2 is 1. However, because C is of fload type, 1 is automatically extended to decimal, that is, 1.000000.