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Constant

  • A constant is a value or identifier whose value is fixed and does not change, in the entire program.
  • Constant is similar to a variable but it can hold only a single variable during the execution of program.
  • Ex: const double PI = 3.14;
    Here,

    • Const is a identifier
    • Double is a data type
    • PI is a constant variable name that takes a value of 3.14.
    • This value of 3.14 does not change during the entire program.

Variable

  • Variable is any characteristic, number, or quantity that can be measured or counted.
  • It is also called as data item.
  • A Variable is a name or an identifier that can store any values, and those values can be changed at any time during the program.
  • For example: int score = 6;
    • Here, score is a variable name of integer type that stores the value 6. The value of score can be changed any time during the program.

 

 

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What are the advantages and disadvantages of using inline and const

Inline:

Advantages:

  • It does not require function calling overhead.
  • It additionally save overhead of variables push/pop on the stack, while function calling.
  • It also save overhead of return call from a function.
  • It increases locality of reference by utilizing instruction cache.
  • Inline function may be useful (if it is small) for embedded systems because inline can yield less code than the function call outline and return.

Disadvantages:

  • If you use too many inline functions then the size of the binary executable file will be large, because of the duplication of same code.
  • Too much inlining can also reduce your instruction cache hit rate, thus reducing the speed of instruction fetch from that of cache memory to that of primary memory.
  • It may cause compilation overhead as if somebody changes code inside inline function than all calling location will also be compiled.

Const:

Advantages:

  • If you want any variable to keep constant through out the program then you can use const keyword.
  • It is stored in the read only of the initalized data segment , even the pointer storing it’s location cannot change the value of it, pointer can just change the address to point at some other location.

Disadvantages:

  • As the const is not flexible so mostly people use #define which is more flexible than const.
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