Maybe I just need to explain the statement to you: "pad=sum++,pad++,++pad;" (the original text is missing a semicolon!), this is an assignment statement as a whole, the assignment number " =” On the left is an integer variable, and on the right is a comma statement. A comma statement will also have a value. It first calculates each statement separated by commas from front to back (for example, in this example, sum++ is calculated first, and then Calculate pad++, and finally ++pad; in this way, the value of sum first becomes 6, then the value of pad becomes 6, and then becomes 7. This is how pad=7 is generated!