Could someone explain clearly about this?

Question

the output of the codes are different.
That is:
for(int x=1;x<=5;x++)
{ for(int y=1;y<=3;y++)
{ Console. Write("a");
}
Console.WriteLine();
}
Output :
aaa
aaa
aaa
aaa
aaa
That is 3a and five times loop running
But when I put 'x' in inner most loop instead of '1' (int y=x; y<=3; y++)
output :
aaa
aa
a
The output is different. x also equal to 1, y=x=1.So, why the output is different. That's really make me confuse.