C语言中数组的一些基本知识小结

int ages[3] = {4, 6, 9};
int nums[10] = {1,2}; // 其余的自动初始化为0
int nums[] = {1,2,3,5,6}; // 根据大括号中的元素个数确定数组元素的个数
int nums[5] = {[4] = 3,[1] = 2}; // 指定元素个数,同时给指定元素进行初始化
int nums[3]; nums[0] = 1; nums[1] = 2; nums[2] = 3; // 先定义，后初始化

int ages['A'] = {19, 22, 33};

printf("ages[0] = %d\n", ages[0]);

int ages[5 + 5] = {19, 22, 33};

printf("ages[0] = %d\n", ages[0]);

int ages['A' + 5] = {19, 22, 33};

printf("ages[0] = %d\n", ages[0])

int a[]; // 错误

int number = 10;

int ages[number]; // 不报错, 但是没有初始化, 里面是随机值
  > int number = 10;
  > 
  > int ages[number] = {19, 22, 33} // 直接报错

 - > int ages10[5];
  > 
  > ages10 = {19, 22, 33};  // 错误。只能在定义数组的时候进行一次性（全部赋值）的初始化

void printMyArray(int myArray[]) {
   int length = sizeof(myArray) / sizeof(myArray[0]);
   for(int i = 0; i < length; i++) {
    printf("%i", myArray[i]);
   }
}

int main() {
  int myArray[5] = {1,2,3,4,5};
  printMyArray(myArray);
  return 0;
}

void printMyArray(int myArray[], int length) {
  for(int i = 0; i < length; i++) {
    printf("%i ", myArray[i]);
  }
}

int main(int argc, const char * argv[]) {
  int myArray[5] = {1,2,3,4,5};
  int length = sizeof(myArray) / sizeof(myArray[0]);
  printMyArray(myArray, length);
  return 0;
}

// 空间换时间, 适合数据比较少
//  1.定义数组,保存用户输入的整数
//  一定要给数组初始化, 否则有可能是一些随机值
  int numbers[10] = {0};
//  2.接收用户输入的整数
//  2.1定义变量接收用户输入的整数
  int index = -1;
  for (int i = 0; i < 6; i++) {
    printf("请输入第%d个整数\n", i + 1);
    scanf("%d", &index);
//    将用户输入的值作为索引取修改数组中对应的元素的值为1
//    指针的时候回来演示刚才的问题
    numbers[index] = 1 ;
  }

  int length = sizeof(numbers) / sizeof(numbers[0]);
  for (int i = 0; i < length; i++) {
    if (1 == numbers[i]) {
      // 输出索引
      printf("%d", i);
    }
  }

//  1.定义数组,保存用户输入的整数
  int numbers[10] = {0};
//  2.接收用户输入的整数
//  2.1定义变量接收用户输入的整数
  int index = -1;
  for (int i = 0; i < 6; i++) {
    printf("请输入第%d个整数\n", i + 1);
    scanf("%d", &index);
//    将用户输入的值作为索引取修改数组中对应的元素的值为1
//    假设 用户输入的是 1,1,1,2,2,2
    numbers[index] = numbers[index] + 1 ;
  }

  int length = sizeof(numbers) / sizeof(numbers[0]);
  for (int i = 0; i < length; i++) {
//    j = 1 因为如果数组元素中存储的值是0不用输出
//    将i对应存储空间中的元素取出,判断需要输出几次
    for (int j = 1; j <= numbers[i]; j++) {
      printf("%d", i);// 1 1 1 2 2 2
    }
  }

void selectSort(int numbers[], int length) {
  for (int i = 0; i < length; i++) {
    for (int j = i + 1; j < length; j++) {
      if (numbers[i] < numbers[j]) {
        int temp = numbers[i];
        numbers[i] = numbers[j];
        numbers[j] = temp;
      }
    }
  }
}

int main(int argc, const char * argv[]) {
  int myArray[] = {42, 7, 1, -3, 88};
  int length = sizeof(myArray) / sizeof(myArray[0]);
  selectSort(myArray, length);
  for (int i = 0; i < length; i++) {
    printf("%i ", myArray[i]);
  }
  return 0;
}

void bubbleSort(int numbers[], int length) {
  for (int i = 0; i < length - 1; i++) {
    for (int j = 0; j < length - i - 1; j++) {
      if (numbers[j] > numbers[j + 1]) {
        int temp = numbers[j];
        numbers[j] = numbers[j + 1];
        numbers[j + 1] = temp;
      }
    }
  }
}

int main(int argc, const char * argv[]) {
  int myArray[] = {42, 7, 1, -3, 88};
  int length = sizeof(myArray) / sizeof(myArray[0]);
  bubbleSort(myArray, length);
  for (int i = 0; i < length; i++) {
    printf("%i ", myArray[i]);
  }
  return 0;
}

int binSearch(int myArray[], int length, int key) {
  int index = -1;

  int max = length - 1;
  int min = 0;
  int mid = (max + min) / 2;

  while (min <= max) {
    if (myArray[mid] > key) {
      max = mid - 1;
    } else if (myArray[mid] < key){
      min = mid + 1;
    } else if (myArray[mid] == key) {
      index = mid;
      break;
    }
    mid = (max + min) / 2;
  }

  return index;
}

int main(int argc, const char * argv[]) {
  int myArray[] = {-3, 1, 7, 42, 88};
  int length = sizeof(myArray) / sizeof(myArray[0]);
  int index = binSearch(myArray, length, 88);
  printf("index: %i ", index);
  return 0;
}