1. Topic: there are n people in a circle, ranking in order, reporting numbers from the first (from 1 to 3). If the person who reports to 3 exits the circle, the last one left is the one with the original number.
Tip: complete with array

#include <stdio.h>
#define N 100
int fun (int n, int m );//Declarative statement
int main()
{
	int n,m;
	printf("Please enter the number of people (the maximum is 100):\n");
	scanf("%d",&n);
	printf("please input m:\n");
	scanf("%d",&m);
	fun(n,m) ;//Call the fun function
    return 0;
}
int fun(int n,int m)
{
	int a[N];//The maximum number of people allowed to enter is 100
	int i, count = n;//i is to set the number of cycles
    int cnt = 0;//b is used to count 3. When the count reaches 3, return to zero.
// int left = 0;
	for(i = 0;i < n;i++)
	{
		a[i] = i+1;//Assign value to a[i], from 1 to n
	}
	while (count != 1)//It means that there is no cycle until the last one is left.
	{
		for (i = 0;i < n ;i++)
		{
			if(a[i] == 0)
			{
				continue;//After the second round, skip counting for the person whose previous round is assigned to 0
			}
			cnt++;
			if (cnt == m)//Assign a value of 0 to the person whose count is full of 3
			{
				cnt = 0;
				a[i] = 0;
				count--;//count is actually the number of people removed
			}
		}
	}
	for(i = 0;i < n; i++)
	{
		if(a[i] != 0)
		{
			printf("The number of the remaining people is:\n");
			printf("%d\n",a[i]);
		}
	}
}

2. Title: write a C function to invert "I am from shanghai" to "shanghai from am I", that is, to invert the word position in the sentence without changing the internal structure of the word.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main()
{
    char *str[] = { "I", "am","from","shanghai" ,NULL};
    int i = 0;
    int j = 0;
    int len  = 0;
    char *temp;
    while (str[i] != NULL)
    {
        i++;
        len++;
    }
    for(i = 0, j = len - 1; j  > i; i++,j--)
    {
        temp =*(str+i);
        *(str+i) = *(str+j);
        *(str+j) = temp;
    }
    for(i = 0; i < len; i++)
    {
        printf("%s ", *(str+i));
    }
    printf("\n");

    return 0;
}

3. Title: input a string, and input the frame header and frame footer (can be multiple characters) to recognize the legal frames in the string.
Tip: the frame header and the frame tail are the head and tail strings respectively, and the head hauboisoktail in "asd headhauboisoktail" is the legal frame.

#include <stdio.h>
int main()
{
char *str[] = {"head", "tail"};
char p[100];
printf ("Please enter a string( < 100)\n");
fgets (p, 100, stdin);

int i = 0;
int j = 0;
int index = 0; // Subscript of i
char *p1 = p;
int m = 0;
int flag = 0, s = 0;// Flag bit
for (; i < 100; i++ )
{
    while (j < 4)
    {
        if (p[i] == str[m][j]) 
          {  
             flag = 1;
             s = m;
             i++;
             j++;
              
          }
        else 
        {
            s = 0;
            flag = 0;
            break;
        }
    }  
   if (s == 1  && flag == 1)
   {          
       p[i] = '\0';
       break;          
   }
                  
   if (flag == 1 && m == 0)
   {
       p1 = &p[i - j];
       m = m + 1;   
       j = 0;
    }
    

}
                  
printf ("%s\n", p1);  
return 0;
}