main 入口点
了解脚本为何从 main 函数开始
main 入口点 是 CoddyKit 上的免费 Mojo Academy 课时。 这是第 2 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Mojo Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Mojo Academy 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Every Program Needs a Start
When you run a Mojo file, the program needs to know where to begin. That starting point is a special function named main. 🚀
Mojo Looks for main
The toolchain searches your file for a function called main and calls it for you. You never call main yourself.
def main():
print("Program started")The Entry Point Idea
An entry point is simply where execution enters your code. In Mojo that door is always main, so your logic goes inside it.
Code Outside main
Top-level definitions like functions and structs can live outside main, but the work that actually runs starts from main.
fn greet():
print("Hi")
def main():
greet()main Takes No Arguments
A basic main needs no parameters. The empty parentheses after the name show it accepts nothing when Mojo calls it.
def main():
print("No args needed")One main Per Program
A program has exactly one main. Two would confuse Mojo about where to begin, so the compiler expects a single clear entry point.
def or fn for main
You can define main with def or fn. Both work as the entry point; def is the friendlier, Python-like choice when starting out.
fn main():
print("Strict style")Order Inside main
Statements inside main run top to bottom, in order. The first line executes first, then the next, building your program step by step.
def main():
print("first")
print("second")Calling Helpers from main
main is often short: it just calls other functions. This keeps your entry point a clean summary of what the program does.
def main():
setup()
run()Forgetting main
If a file has no main, running it as a program fails because Mojo cannot find where to start. Always include one for runnable files.
main Ends the Program
When the last line of main finishes, the program is done and control returns to your shell. No extra cleanup is required.
Quick Check
You wrote a Mojo file with several functions. Where does execution actually begin?
Recap
Every runnable Mojo file needs one main function. Mojo calls it to start, runs its lines in order, and ends when main finishes. 🎯
常见问题解答
「main 入口点」课时是免费的吗？
是的 — 「main 入口点」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Mojo Academy 课程的其余内容，请升级到 CoddyKit PRO。 Mojo Academy 课程共包含 4 节课。
「main 入口点」这节课中我会学到什么？
了解脚本为何从 main 函数开始 你通过在浏览器中直接运行的动手代码来练习 Mojo Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Mojo Academy 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Mojo Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 2 节课，共 4 节。
「main 入口点」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Mojo Academy 课中编写并运行代码吗？
能。每节 Mojo Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。