details make a difference

Use flags with caution (I am a novice in microcontrollers, experts please help me, welcome to give me advice!~)
What I am talking about here is to use flags reasonably and carefully, otherwise it is easy to make mistakes and difficult to debug.
When I was working today, I modified the timer timing function and gained experience. What I said here has nothing to do with the specific microcontroller, it is a general idea.
Take what I modified today as an example:
The two I/O pins of the PIC microcontroller control the on and off of two LED lights (blue and red lights, respectively, LEDs are used here to avoid involving company content).
The requirements are that
the blue light turns on once every 5s, for about 100ms;
the red light turns on once every 10s, for 100ms each time;
the red and blue lights are staggered as much as possible.
My idea is
to define a 10s time axis and use a timer to implement it, turning on the blue light at 2.5 seconds and 7.5 seconds, and turning on the red light at 10s.
There is a global variable cnt.

Define a global variable times = 0.

[cpp]  view plain  copy  print ?

1. 0 2.5s 5s 7.5s 10s  

2. |-------------|===|-------------|-------------|=== |-------------|+++|  

3.                blue blue red  

4. |----times=0------|----------times=1----------|----times=0---- -------|  

I took it for granted that this would work, but I didn’t
know there was a
bug here, because this condition is also met between 7.5 and 10 s . . . The system that comes out like this is not what we want above. We should change it to if((cnt > 250)&&(times == 0)&&(cnt < 750)) so that it will work. . .