###### tags: `Basic`
- [x] check
# a005: Eva's homework
:::info
Eva is doing her math homework about fill-in-the-blank question. The rule are give you four integer and you have to fill in the fifth integer. Because the sequence is ether arithmetic sequence or geometric sequence. Please write a program to finish the homework.

| input | output |
| -------- | -------- |
| 2 | |
| 1 2 3 4 | 1 2 3 4 5|
| 1 2 4 8 | 1 2 4 8 16|

:::

### 1st Ideas of solving a problem(slowly)
>1. Because we should check the sequence is arithmetic or geomaetric sequence, we should use 'int' rather than 'char' to read the input data.
>2. In main function, use a forloop to control how many sequences we should judge.
>3. In the forloop, use if/else to check the sequence is arithmetic or geomaetric and print the sequence.

#include<stdio.h>

int main(){
    int input,i,a,b,c,d,e;
    scanf("%d",&input);
    if(input!=0){
        for(i=1;i<=input;i++){
            scanf("%d%d%d%d",&a,&b,&c,&d);
            if((c-b)==(b-a)){
                e=d+(b-a);
            }
            else{
                e=d*(b/a);
            }
            printf("%d %d %d %d %d\n",a,b,c,d,e);
        }
    }
    return 0;

    }
    
    

### 2nd Ideas of solving a problem(fast)
>1. use a function named 'judge'.

#include<stdio.h>
int judge(int,int,int);
int main(){
    int input,i,a,b,c,d;
    scanf("%d",&input);
    if(input!=0){
        for(i=1;i<=input;i++){
            scanf("%d%d%d%d",&a,&b,&c,&d);
            printf("%d %d %d %d ",a,b,c,d);
            printf("%d\n",judge(b,c,d));
        }
    }
    return 0;

    }

    int judge(int b,int c,int d){
        int e;
        if((d-c)==(c-b)){
                e=d+(c-b);
            }
        else{
                e=d*(c/b);
            }
        return e;
    }