A constant expression is a formula with only constants in the expression. For example, 1+2 is a constant expression. If a is defined as a constant 1, then a+2 is also a constant expression. If the variable A is defined, then a+2 is not a constant expression. N=5 is a constant expression.

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Constant, although it serves the hardware, software and programming language in computer technology, is not a concept specially introduced for hardware, software and programming language. Constants can be divided into different types, for example, 25 and 0 are integer constants, 6.8 is a real constant, and A and B are character constants. Constants can usually be judged from their literal forms. This constant is called literal constant or direct constant.

When discussing the relationship between function values and independent variables, there are often one or more constants in a function. People focus on the laws of these changes, and it is often easy to find the correct reflection of the development laws of things in their brains.

A popular metaphor of constant-just as mountains are not easy to change, of course, when the ocean dries up and rocks crack, the acceleration of gravity on the earth will also change; The constant used by people is a quantity that will not change for a long time. The speed of light in vacuum is constant, theoretically constant and constant.