1#include <stdio.h>
2int main(){
3    printf("Hello world!");
4    return 0;
5}

1#include <stdio.h>
2int main(){
3    int a, b;
4    scanf("%d %d", &a, &b);
5    printf("%d", a + b);// C 改成 a - b, D 改成 a * b
6    return 0;
7}

 1#include <stdio.h>
 2int main(){
 3    double a, b;
 4    double c;
 5    scanf("%lf %lf", &a, &b);
 6    if(b == 0)  printf("False");
 7    if(b != 0) {
 8        c = a / b;
 9        printf("%.2lf", c);
10    }
11    return 0;
12}

 1#include <stdio.h>
 2int main(){
 3    int i;
 4    scanf("%d", &i);
 5    if(i > 100){
 6        printf("False!");
 7    }else if(i >= 90){
 8        printf("A");
 9    }else if(i >= 80){
10        printf("B");
11    }else if(i >= 70){
12        printf("C");
13    }else if(i >= 60){
14        printf("D");
15    }else if(i >= 0){
16        printf("E");
17    }else{
18        printf("False!");
19    }
20    return 0;
21}

 1#include <stdio.h>
 2#include <math.h>
 3int  main(){
 4  double  a, b, c, p, s;
 5  scanf ( "%lf %lf %lf", &a, &b, &c);
 6  if (a + b > c && a + c > b && b + c > a)
 7  {
 8    p = (a + b + c) / 2;
 9    s = sqrt(p * (p - a) * (p - b) * (p - c));
10    printf ( "%.2lf\n", s);
11  }
12  else  printf ("Fail\n");
13  return  0;
14}

 1#include <stdio.h>
 2#include <math.h>
 3int main(){
 4    float d;
 5    int x1, y1, x2, y2;
 6    scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
 7    d = sqrt((float)(x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
 8    printf("%.2lf", d);
 9    return 0;
10}

1#include <stdio.h>
2#include <math.h>
3int main(){
4    float a;
5    scanf("%f", &a);
6    printf("%.2f", fabs(a));
7    return 0;
8}

1#include <stdio.h>
2int main() {
3	double a;
4	double b;
5	scanf("%lf %lf", &a, &b);
6	printf("%d", (int)((a + b / 10) / 1.5));
7	return 0;
8}