Almost certainly you have:
Thing account1[6] = { ... };
for (i = 0; i <= 6; i++)
{
if ([user1 isEqualToString:account1[i].name])
and the compiler knows that <= 6
will go beyond the bounds of the array (last index is 5 not 6).
To correct:
for (i = 0; i < 6; i++)
^
solved Objective-C programming [closed]