求简单函数!!!!用C++编写!!用最简单的写啊!!谢谢了!!

1.
double area(double r){return 3.1415926*r*r;}
2.
bool root(double a, double b, double c, double &x1, double &x2)
{
if(b*b<4a*c) return false;
x1=(sqrt(b*b-4a*c)-b)/(2*a);
x2=(-sqrt(b*b-4a*c)-b)/(2*a);
return true;
}
3.
int min(int a, int b, int c)
{
if(a<=b && a<=c) return a;
if(b<=c && b<=a) return b;
if(c<=a && c<=b) return c;
}
4.
int sum(int *num, int n)
{
int s=0;
for(int i=0;i<n;i++)
{
if(num[i]>0) s+=num[i];
}
return s;
}
5.
int odd(int *num, int n)
{
int s=1;
for(int i=0;i<n;i++)
{
if(num[i]%2) s*=num[i];
}
return s;
}

#include <math.h>
//求圆面积
double calArear(double r){
const double PI=3.14;//PI常量
return PI*r*r;
}

//求2次方程 ax^2+bx+c的实数根,写入X1,X2
void formula(double a,double b,double c,double * X1,double X2)
{