1. Input an integer n, and then input n groups of subscript sequence number and string in turn. It is required to delete the characters corresponding to the sequence number subscript of the string and output them in turn.

#include<stdio,h>
int main(){
    int n,index[100],i,j;
    char str[100][100];
    
    scanf("%d",&n);
    for(i=0;i<n;i++){
         scanf("%d",&index[100]);
         getchar();
        gets(str[i]);
   }
   for(i=0;i<n;i++){
       j=index[i];
       while(str[i][j]!='\0'){
           str[i][j]=str[i][++j];
       }
       puts(str[i]);
       printf("\n");
   }
}

2. Define a floating-point array with a capacity of 10. It is required to output the average value of these 10 numbers, and then arrange the elements larger than the average value in the first place in the original order, and the elements smaller than the average value in the last place in the original order (the result is reserved for one decimal place).

#include<stdio.h>
int main(){
    float num[10],ave=0.0,res[10];
    int i,j=0,k=4;
    for(i=0;i<10;i++){
        scanf("%d",&num[i]);
        ave+=num[i];
    }
    ave/=10;
    printf("%f\n",ave);
    for(i=0;i<10;i++){
        if(num[i]>ave){
            res[j++]=num[i];
        }else{
            res[k++]=num[i];
        }
    }
    res[k]='\0';
    puts(res);
    return 0;
}

3. Enter three 3-bit integers, and then output a new number. Its hundreds are the hundreds of the first number, its tens are the tens of the second number, and its bits are the ones of the third number.

#include<stdio.h>
int main(){
    int a,b,c;
    int d,e,f;
    scanf("%d %d %d",&a,&b,&c);
    d=a/100;
    e=(b%100)/10;
    f=c%10;
    printf("%d%d%d",d,e,f);
}

4. Input An integer n, calculate and output the general term of the sequence An: A1=1, A2=1 / (1+A1),..., An=1 / (1+An-1)

#include<stdio.h>
int main(){
    double A=1.0;
    int i,n;
    scanf("%d",&n);
    for(i=1;i<n;i++){
        A=1/(1+A);
    }
    printf("%.7lf",A);
    return 0;
}

5. Input a long integer, calculate and output the product of its digits

#include<stdio.h>
int main(){
    long n,result;
    scanf("%ld",&n);
    while(n){
        result *= n%10;
        n /= 10;
    }
    printf("%ld",result);
    return 0;
}

6.

7.

8. Input three integers and output them in order of small to large

#include<stdio.h>
int main(){
    int a,b,c,t;
    scanf("%d %d %d",&a,&b,&c);
    if(a>b){
        t=a;
        a=b;
        b=t;
    }
    if(b>c){
        t=c;
        c=b;
        b=t;
    }
    if(a>c){
        t=a;
        a=c;
        c=t;
    }
    printf("%d %d %d",a,b,c);
    return 0;
}

9. Define and output one-dimensional integer array (input n first, then input n integers), input an integer m, and output a new n-dimensional array. It is required that the elements starting from the subscript m (including m) are put in front of the array in the original order, and the previous m items are put behind the array in the original order.

#include<stdio.h>
int reverse(int num[],int start,int end){
    int temp;
    for(;start<end;start++,end--){
        temp=num[start];
        num[start]=num[end];
        num[end]=temp;
    }
}
int main(){
    int n,m,i;
    int num[100];
    scanf("%d",&n);
    for(i=0;i<n;i++){
        scanf("%d",&num[i]);
    }
    scanf("%d",&m);
    reverse(num,0,m-1);
    reverse(num,m,n-1);
    reverse(num,0,n-1);
    for(i=0;i<n;i++){
        printf("%d ",num[i]);
    }
    return 0;
}

10. Enter a 3-bit integer, invert its number and output

#include<stdio.h>
int main(){
    int n,a,b,c;
    scanf("%d",&n);
    a=n%10;
    b=(n/10)%10;
    c=n/100;
    printf("%d%d%d",a,b,c);
    return 0;
}

11. Input an integer n, find the value of Sn=1-1/2+1/3-1/4+...+(-1)^(n+1)/n and output

#include<stdio.h>
int main(){
    int sign=1;
    int i,n;
    double Sn=1;
    scanf("%d",&n);
    for(i=2;i<=n;i++){
        sign*=-1;
        Sn+=1.0/n*sign;
    }
    printf(".6lf",Sn);
    return 0;
}

12. Input a string from the keyboard, convert all its uppercase letters to lowercase, lowercase English letters to uppercase, and output the result (other characters remain unchanged)

#include<stdio.h>
int main(){
    int ch;
    while(ch=getchar()!='\n'){
        if(ch>='A'&&ch<='Z'){
            ch+=32;
        }else if(ch>='a'&&ch<='z'){
            ch-=32;
        }
        printf("%c",ch);
    }
    return 0;
}

13.

14.

15. Input an integer n and output the sum of the first n terms of Fibonacci series

#include<stdio.h>
int main(){
    int i,n,f1=1,f2=1,f,sum=2;
    scanf("%d",&n);
    if(n==1)
        sum=1;
    else if(n==2)
        sum=2;
    else
        for(i=3;i<=n;i++){
            f=f1+f2;
            f1=f2;
            f2=f;
            sum+=f;
        }
    printf("%d",sum);
    return 0;
}

16. Input the first term a, common ratio q, number of terms n of a sequence, and output the sum of the first n terms.

#include<stdio.h>
#include<math.h>
int main(){
    double a,q,Sn=0;
    int n,i;
    scanf("%lf %lf %d",&a,&q,&n);
    for(i=1;i<=n;i++){
        Sn+=a*pow(q,i-1);
    }
    printf("%.0lf",Sn);
    return 0;
}

17. In the form of a linked list, two strings are connected and output.

#include<stdio.h>
typedef struct node{
    char data;
    struct node *next;
}LinkList;
int main(){
    LinkList *head,*node,*end;
    head=(LinkList*)malloc(sizeof(LinkList));
    end=head;
    while(ch=getchar()!='\n'){
        node=(LinkList*)malloc(sizeof(LinkList));
        node->data=ch;
        end->next=node;
        end=node;
    }
    while(ch=getchar()!=\n){
        node=(LinkList*)malloc(sizeof(LinkList));
        node->data=ch;
        end->next=node;
        end=node;
    }
    end->next=NULL;
    while(head->next!=NULL){
        head=head->next;
        printf("%c",head->data);
    }
    return 0;
}

18.