C :

#include<stdio.h>
#define MAX(a,b,c) ((a>b)?a:b)>c?((a>b)?a:b):c
int main()
{
    float a,b,c;
    scanf("%f%f%f",&a,&b,&c);
    printf("%.3f\n%.3f\n",MAX(a,b,c),MAX(a,b,c));
    return 0;
}

C++ :

#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
int main()
{
    double a[3];
    cin>>a[0]>>a[1]>>a[2];
    sort(a,a+3);
    printf("%.3lf\n",a[2]);
    printf("%.3lf\n",a[2]);
    return 0;
}