6.4 return

• Statement return; is only valid if the function return type is void.
• Just finish the execution of the function, no value returned.

如果函数的返回值类型为void，就不需要返回具体的返回值，直接结束即可。

| ```cpp void print_gender(bool isMale) { if(isMale) cout << “Male” << endl; else cout << “Female” << endl; return; }

 | ```cpp
void print_gender(bool isMale)
{
    if(isMale)
        cout << "Male" << endl;
    else
        cout << "Female" << endl;
}

| | —- | —- |

• The return type can be a fundamental type or a compound type.
  • 既可以是基本数据类型，也可以是组合数据类型
• 返回值的方式是：Pass by value:
  • Fundamental types: the value of a constant/variable is copied
  • Pointers: the address is copied
  • Structures: the whole structure is copied

    float maxa = matrix_max(matA);
    Matrix * pMat = create_matrix(4,5);
    

    ```cpp Matrix create_matrix(int rows, int cols) { Matrix p = new Matrix{rows, cols}; p->pData = new float[p->rows * p->cols]{1.f, 2.f, 3.f}; // you should check if the memory is allocated successfully // and don’t forget to release the memory return p; }

- If we have a lot to return，Such as a matrix addition function (A+B->C)
   - 如果有很多内容需要返回
- A suggested prototype:
   - To use `references` to avoid data copying
   - To use `const` parameters to avoid the input data is modified
   - To use non-const reference parameters to receive the output
```cpp
bool matrix_add(const Matrix & matA, const Matrix & matB, Matrix & matC)
{
    // 1. check the dimensions of the three matrices
    // 2. re-create matC if needed
    // 3. do: matC = matA + matB
    // 4. return true if everything is right
}