PREFACE

在 Data stucture and Algorithm 的 git 项目学到的：

这如果是0，就是真注释，代码不运行，如果是1，代码运行

#if 0
#endif
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如：

#if 1
int IsLess(int a, int b) {
    return a < b;
}

int IsLarger(int a, int b) {
    return a > b;
}

// Define a function pointer type, which points to a function
typedef int (*ComparatorFuncPtr)(int, int);


void BubbleSort2(int *ptr, int n, ComparatorFuncPtr compare) {
    for (int iMax = n - 2; iMax >= 0; iMax--) {
        for (int i = 0; ____Q1_____; _____Q2____) {
            if (_____Q3_____) {
                ____Q4____;
            }
        }       
    }
}

int TestBubbleSort2(void) {    
    int arr[] = {30, 50, 20, 10, 60, 40};
    int len = sizeof(arr) / sizeof(arr[0]);

    // a function pointer variable which points to the function IsLarger()
    ComparatorFuncPtr fptr = &IsLarger;    
    printf("Before sorting:\n");
    PrintArray(arr, len);
    BubbleSort2(arr, len, fptr);
    // in ascending order
    printf("After sorting:\n");
    PrintArray(arr, len);

    // a function pointer variable which points to the function IsLess()
    fptr = ____Q5____;    
    printf("\nBefore sorting:\n");
    PrintArray(arr, len);
    BubbleSort2(arr, len, fptr);
    // in descending order
    printf("After sorting:\n");
    PrintArray(arr, len);
    return 0;
}
#endif
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