#include <iostream.h>
#include <math.h>

double max(double x,double y);

void main()
{
double a,b,c;
cout<<"input two numbers:\n";
cin>>a>>b;
c=max(a,b);
count<<"the squart of maximum="<<sqrt(c);
}

double max (double x, double y)
{
if(x>y)
return x;
else
return y;
}

粗心啊你!!!!!
把count<<"the squart of maximum="<<sqrt(c);改为
cout<<"the squart of maximum="<<sqrt(c);
搞定.

把手指　用刀削小些
或是把心放大些
就不会有这样的错误了