Q:

Using multiple integers with one operand in a C conditional statement possible?

Is it possible in C to write something like?  and if so how is it done?
if ( x != 1, 2, 7, 8, 90)

A:

You can't compare multiple values that way.  You need to check each individually combined with the proper logical operator:
if ((x != 1) && (x != 2) && (x != 7) && (x != 8) && (x != 90)

What you wrote is something entirely different.  This:
if ( x != 1, 2, 7, 8, 90)

Is a single comparison operator followed by several instances of the comma operator.  The comma operator evaluates the left operand, discards the value, then evaluates the right operand and takes its value.
So that expression first evaluates x != 1 which will result in either 0 or 1.  That value is discarded and the value 2 is evaluated.  That value is in turn discarded and the next value (7) is evaluated.  Then 8 is evaluated and discarded, then 90 is evaluated which becomes the value of the entire expression.

