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Fixed values that don’t change are constants. A constant is a value chosen in the program and kept the same throughout execution, so it can’t be altered later by the code. This helps prevent unintended changes and makes the program’s intent clear, such as using a constant for π or a maximum limit.

Data types describe what kind of data can be stored (numbers, text, etc.), not whether a value stays fixed. An integer is a numeric data type for whole numbers, and a real is a numeric data type for numbers with decimals. While those describe kinds of numbers, they don’t specify immutability.