% is used to escape in the output string, and the output content depends on the characters after it. For example, %d means that the output is an integer, while %s outputs a string, so if you want to output%, you must add a% after%. Similarly, there are characters' \', \ adding N means output line feed, \ adding T means output tab (tab key) and so on, so if you want to output A, you must add a \ after \ to output A \