What is the difference between #define and constant in C?

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Sumanth Mv

#define used to define a variable that is pre-processed(before compilation) where as constant is a keyword used to declare constant variable which cannot be varied
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#define is a preprocessor directive and is resolved/replaced before the compilation step. So that means if you have like #define PI 3.42 --- during pre-processing (before compilation) imagine as if the compiler actually does a FIND and REPLACE inside your code and finds PI and replaces it with 3.42....
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#define is a preprocessor directive and is resolved/replaced before the compilation step. So that means if you have like #define PI 3.42 --- during pre-processing (before compilation) imagine as if the compiler actually does a FIND and REPLACE inside your code and finds PI and replaces it with 3.42. So there is no way that you can change a value in the program. The constants on the other hand also remain constant throughout the program but hold the memory as well as are resolved at the run time. Let me know if that resolves your query or I can make you understand it the memory way. read less
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#define A B tells the preproccessor (a part of the compiler) to substitute B wherever it sees A in the code, and it does it before compiling the code. A const variable means that once the variable is set it can't be changed.
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