some students in my class are leaving CS because programming is difficult and think that it will not give them bright future. how to motivate that students, that their interest is develop in programming and they become satisfied for their future.
This might be a mistake, actually. Everyone is different. People like doing different things. Programming isn't for everyone, nor is the wider world of Computer Science as a whole. My daughter, for example, is perfectly happy as a Philosopher. My son is perfectly happy outside academia.
Convincing someone to do something (a kind of advertising) may do them harm in the long run. People spend millions of dollars convincing people to consume sugary drinks, to their detriment.
If you make the classes interesting, with interesting problems to solve, those who want to do it will stay. Wish the others well and focus on those who want to work at it. Some of us have found that group work (pair programming) is a motivator, introducing a social aspect to learning as well. On the other hand, it is possible to make learning programming as dull and demotivating as learning multiplication tables.
I'll note that many things are hard. Becoming an olympic athlete is hard. Some people are willing to put in the work to do it. For others, it isn't worth that effort.
Saying the "future is bright" is something you can't honestly predict. Many things could happen that make it less bright. The need for people specializing in CS might decline in future years as some processes become more regularized. This has been the history of the world, actually. One takes a chance on the future no matter what you do, so you might as well follow your own dreams, not those of someone else.
I used to teach adults (most well after college age) programming so they could get jobs after a disability caused them to leave their previous job. They were highly motivated to learn enough in one year to get hired.
What I focussed on was to make their learning free of unnecessary difficulty by pointing out the usual problem areas and trying to make my explanations direct, clear, memorable and interesting.
Your excitement about programming will interest them. Some will drop out, but that is not your issue. For any problems you cannot directly solve in your classroom, get help from the administration, and just focus entirely on your part, which is to teach and assist.
Be sure to explain that at times programming IS difficult and frustrating, and sometimes we have to choose a different way of solving a problem. Usually later it can be changed when a better solution is seen.
That's the best advice I have for you. Good luck!
Do you maintain contact with your former students? I have a sizeable number of former students earning nice livings at places such as Apple, Microsoft, Google, Facebook, and YouTube. Others are in great graduate programs. Some are academics at places such as Stanford, UMiami, and UMaryland.
They are doing very well. I use my network to benefit my current and former students. It's quite powerful. And it serves as a beacon to my present students.