Stability of functional equations in single variable ✩

This paper discusses Hyers–Ulam stability for functional equations in single variable, including the forms of linear functional equation, nonlinear functional equation and iterative equation. Surveying many known and related results, we clarify the relations between Hyers–Ulam stability and other senses of stability such as iterative stability, continuous dependence and robust stability, which are used for functional equations. Applying results of nonlinear functional equations we give the Hyers– Ulam stability of Böttcher’s equation. We also prove a general result of Hyers–Ulam stability for iterative equations.  2003 Published by Elsevier Inc.