macOS Beginner in Xcode

[Becutan]

I was assigned by my professor to exercise in C++ but I kind of refuse to work on a Windows at home so I am working on the latest version of Xcode.
I am writing a simple beginners program, a grading program but I am stuck.
So, I open up command line tool in application and a C++ file when I open a new file and write the code. But here comes the tricky part for me and I bet it's an incredibly stupid thing I am missing but Xcode gives me the following error: "Linker command failed with exit code".
What is the problem? Can anyone help me out somehow?

I know you read these kind of stupid things everyday and it would be a cliche if I said, please try to understand me I am a beginner so I won't

 

[robvas]

What action are you performing when you get that error message?

 

[Becutan]

What action are you performing when you get that error message?

when I try to build the code. I can't build it nor I can run it, which is understandable..

 

[Sonnestah]

Post your code so we can help further