Click keil settings, as shown below:
1. Set prompt form
None: Do not prompt.
Vertical Line: Dotted line prompt.
As shown by the lines in the red box, codes exceeding three lines exceed the set number of characters.
Colored Background: Highlight tips.
As shown in the red box, the highlighted part of each line of code exceeds the set number of characters.
2. Set the threshold for the number of characters per line. Generally, it can be set to 80 (in the code specification, a maximum of 80 characters per line is generally used).