任務一

#include<stdio.h>
#include<math.h>
int main(){
	float a,b,c,x1,x2;
	float delta,real,imag;
	while(scanf("%f%f%f",&a,&b,&c)!=EOF){
		if(a==0){
			printf("not quadratic equation.\n\n");
		}else{
			delta=b*b-4*a*c;
			if(delta>=0){
				x1=(-b+sqrt(delta))/(2*a);
				x2=(-b-sqrt(delta))/(2*a);
				printf("x1=%.2f,x2=%.2f\n\n",x1,x2);
			}else{
				real=-b/(2*a);
				imag=sqrt(-delta)/(2*a);
				printf("x1=%.2f+%.2fi,x2=%.2f-%.2fi\n\n",real,imag,real,imag);
			}
		}
	}
	return 0;
}

任務二

 1 #include<stdio.h>
 2 #include<stdlib.h>
 3 #include<time.h>
 4 #define N 5
 5 int main(){
 6     int x,n;
 7     srand(time(0)); //缺失此行每次執行數字不在改變
 8     n=0;
 9     do{
10         n++;
11         x=rand()%10;
12         printf("%3d",x);
13     }while(n<N);
14     printf("\n
 
");
15     return 0;
16 }

任務三

#include<stdio.h>
int main(){
    int sum=0;
    int count=0;
    for(int i=101;i<=200;i++){
        int mark=0;
        for(int j=2;j<100;j++){
            if(i%j==0){
                mark=1;
            }
        }
        if(mark==0){
            printf("%d ",i);
            count
 
++;
            if(count%5==0){
                printf("\n");
            }
        }
    }
    printf("%d",count);
    return 0;
}

任務四

#include<stdio.h>
#include<string.h>
int main(){
    char number[50]={0};
    while(scanf("%s",number)!=EOF){
    int len=strlen(number);
    for(int i=0;i<len;i++){
        if((number[i]-'0')%2!=0){
            printf("%c",number[i]);
        }
    }
    getchar();
    memset(number,0,50);
    printf("\n");
}
    return 0;
}

利用字元陣列相當直觀，簡易且不容易出錯。（但注意初始化陣列，getchar（）讀取換行符）

任務五

#include<stdio.h>
#include<math.h>
int main(){
    int n;
    while(scanf("%d",&n)!=EOF){
    double temp=1.0;
    double s=0.0;
    for(int i=1;i<=n;i++){
        if(i%2!=0){
            temp=abs(temp*i);
        }else{
            temp=-(temp*i);
        }
        s+=1.0/temp;
    }
    printf("%lf\n",s);
    }
    return 0;
}

任務六

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main(){
    int x=0,n=0;
    srand(time(0));
    while(x==0){
    x=rand()%31;
    }
    for(int i=0;i<3;i++){
        scanf("%d",&n);
        if(n==x){
            printf("lucky day!");
            break;
        }
        if(n<x){
            printf("too early");
        }
        if(n>x){
            printf("too late");
        }
        printf("\n");
        if(i==2){
            printf("luckday is %d!",x);
        }
    }
    return 0;
}

11.28生日，surprise!