having problem in coding a small system, which can let user to key in the input and save it into txt before checking the txt file whether the data is duplicated or not

I see no code here so I can't comment about the code as it is. Without that and the txt file all I can offer is that you should check for duplicates before saving it to the txt file.

Hello,
As @rproffitt has quoted that we cannot assist you without seeing the code.
So, please share the code so that we can help you in solving your problem
in coding a small system.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.