how to compute square root of a perfect square just using simple addition only

Caution: This methods works just only for perfect squares
#include<stdio.h>
void main()
{
int cnt=0,sum=0,i=1,num;
printf("\n Enter the number for which you want the square root\n");
scanf("%d",&num);
while(sum<num)
{
sum+=i;
i+=2;
cnt+=1;
}
printf("\n The square root of a given no is %d",cnt);
getch();
}