I want to create a var in a for loop, e.g.
for(int i; i<=10;i++)
{
string s+i = \"abc\";
}
This should create variables s0, s1, s2... to
Your first example wouldn't work in any language as you are trying to redefine the variable "i". It's an int in the loop control, but a string in the body of the loop.
Based on your updated question the easiest solution is to use an array (in C#):
string[] s = new string[10];
for (int i; i< 10; i++)
{
s[i] = "abc";
}