这三个题咋写，没听懂C语言

Question

C语言buhui，只会简单加减法，不会做情景题，有没有giegie教教我

Answer 1

#include <stdio.h>
int main()
{
    int a, b, c, d;
    int num;
    scanf("%d", &num);
    a = num / 1000;
    b = (num - a * 1000) / 100;
    c = (num % 100) / 10;
    d = num % 10;
    printf("%d", d * 1000 + c * 100 + b * 10 +a);
    return 0;
}

#include<stdio.h>
#include<math.h>
int main()
{
    double a,b,c,s,area;
    scanf("%lf%lf%lf",&a,&b,&c);
  
    s=(a+b+c)/2;
    area=sqrt(s*(s-a)*(s-b)*(s-c));
    printf("a=%f\nb=%f\nt=%f\n",a,b,c);
    printf("area=%f\n",area);
    return 0;
}

#include<stdio.h>
int main()
{
char c1,c2;
getchar(c1);
getchar(c2);
putchar(c1);
printf("%c\n",c2);
return 0;
}