#include<stdio.h>
#include<math.h>
int main()
{double a[10000];
 int n;
 for(n=1;scanf("%lf",&a[n])!=EOF;n++);
 for(;n>=1;n--)
 {a[n]=sqrt(a[n]);
 printf("%0.4lf\n",a[n]);
 }
 return 0;
}

NO one can tall me that?
what should I do?

Маловато наверно будет 10000.
У меня была размерность больше 100 тыщ...

You should change size of your array...

I think you should use stack,

Just one more semicolon(;).

for(n=1;scanf("%lf",&a[n])!=EOF;n++);

scanf return the number of fields successfully converted and assigned; the return value does not include fields that were read but not assigned. A return value of 0 indicates that no fields were assigned. The return value is EOF for an error or if the end-of-file character or the end-of-string character is encountered in the first attempt to read a character.according to compilor,the result of EOF can be -1.each number or character that you input from the keyboard is ASCII,so the sentence "for(n=1;scanf("%lf",&a[n])!=EOF;n++);" would never be ended.