What is the reason that alternating current cannot be measured by a DC ammeter?

The average value of AC for a complete cycle is zero

Alternating current cannot be measured by D.C ammeter because A.C. current have alternating signs and average value of current for complete cycle is zero and practical frequencies are like 50-60 Hz that means it changes signs more than 100 times a second which is not visible on D.C. ammeters.