题目和结构体初步认识

//求n的阶乘
/*
#include<stdio.h>
int count_n(int n)
{
    int m = 0;
    int sum = n;
    for(m=1;m<n;m++)
    {
        sum=sum*m;
    }
    return sum;
}
//用递归求n的阶乘
int count_n1(int n)
{
    if(n>1)
    {
       return count_n1(n-1)*n;
    }
    else
    {
        return 1;
    }
}
int main()
{
    int n = 0;
    int sum = 0;
    scanf("%d",&n);
    sum = count_n1(n);
    printf("%d",sum);
    return 0;
}
*/

//将数组逆序排列
/*
#include<stdio.h>
#include<string.h>
void reverse_string(char* arr,int sz)
{
    int left = 0;
    int right = sz-2;// 不能写sz-1，因为会把\0也交换，导致结果显示为0；
    while(left<right)
    {
        char tem = arr[left];
        arr[left] = arr[right];
        arr[right] = tem;
        left++;
        right--;
    }
}
void reverse_string1(char* arr1)
{
    int left = 0;
    int right = strlen(arr1)-1;//???为什么能用strlen不能用int sz = sizeof(arr)/sizeof(arr[0])在函数里求；
    while(left<right)
    {
        char tem = arr1[left];
        arr1[left] = arr1[right];
        arr1[right] = tem;
        left++;
        right--;
    }
}
void reverse_string2(char* arr,int sz)
{
    int left = 0;
    int right = sz-2;// 不能写sz-1，因为会把\0也交换，导致结果显示为0；
    while(left<right)
    {
        char tem = *(arr+left);
        *(arr+left) = *(arr+right);
        *(arr+right) = tem;
        left++;
        right--;
    }
}
int my_strlen(int* arr)
{
    int count = 0;
    while(*arr != 0)
    {
        count++;
        arr++;
    }
    return count;
}
int main()
{
    char arr[] = "abcdef";
    int sz = sizeof(arr)/sizeof(arr[0]);
    reverse_string(arr,sz);
    printf("%s\n",arr);
    return 0;
}
*/

//用递归的方法将数组逆序
/*
int my_strlen(char* arr)
{
    int count = 0;
    while(*arr != 0)
    {
        count++;
        arr++;
    }
    return count;
}
void reverse_string0(char* arr)
{
    int len=my_strlen(arr);
    char tem = arr[0];
    arr[0]=arr[len-1];
    arr[len-1] = '\0';
    if(my_strlen(arr)>=2)//写成if(my_strlen(arr+1)>=2)也没问题，??为什么
    reverse_string0(arr+1);
    arr[len-1] = tem;
}
#include<stdio.h>
int main()
{
    char arr[] = "abcd";
    reverse_string0(arr);
    printf("%s\n",arr);
    return 0;
}
*/

//结构体
//struct 结构体关键字 stu 结构体标签  struct stu - 结构体类型
/*
struct stu
{
  char name[20];
  short age;
  char tele[12];
  char sex[5];
}s1,s2,s3;//s1，s2，s3是三个全局的结构体变量
typedef struct stu
{
  char name[20];
  short age;
  char tele[12];
  char sex[5];
}stu;
int main()
{
    struct stu s1;//局部变量.
    stu s2;
    return 0;
}
*/
/*
#include<stdio.h>
struct s
{
    int a;
    char c;
    char arr[20];
    double d;
};

struct t
{
    char ch[10];
    struct s s;
    char* pc;
};

int main()
{
    char arr[] = "hello bit\n";
    struct t t = {"hehe",{100,'w',"hello world",3.14},arr};
    printf("%s\n",t.ch);//hehe
    printf("%s\n",t.s.arr);//hello world
    printf("%lf\n",t.s.d);//3.14
    printf("%s\n",t.pc);//hello bit
    return 0;
}
*/