Tell It by Myself…

Use int xxx to create a function

提取一个可以“重复调用” “单纯朴素”的部分构成一个函数，让 main 函数也看起来更加简洁。

可以减少写很多段几乎一模一样的代码，

代码复制是程序质量不良的体现！

It receives 0 or more parameters and send back 0 or 1 value

Definition

In the beginning of the function for example

void sum(int begin, int end)

The void means what type of value you want to return. It can also be int . In fact, in my first year class, there are a lot of function begin with int.

void here means we don’t return any value.

Use the function

If we want to use the function, we have to write

functionname(function value)

Even if we don’t have function value, still need to write ()

function() is the symbol to tell the computer we are going to use the function!

The Return Value

return means 2 things:

We stop the function
We send back (return) a value

Remember if we use void we can’t use the return with value (you can write function with return, but it is meaningless)

The function has precedence relationship. So we usually write the function before the main function (the machine read the code from top to bottom) ==But , we use a method called Function Prototype == That is, we should

Declare the function at first
Write the function definition at last (even after the main function!)