Because I know this program was saved by default into my current folder, my current directory, so dot slash means run the program called a.out that's right here in my current directory not in, like, a out my applications folder or somewhere else.

程序默认保存在,当前目录下的文件夹，/意味着运行这个名为“a，out“的文件,是我当前目录下的文件，而不是应用程序文件夹或其他别的地方的。

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