What is the role and purpose of the 'const' keyword in programming languages?

The keyword const in C/C++ is used to declare constant values or pointers that cannot be changed after initialization. It helps improve code safety by preventing accidental data modification.

Main uses:

• Declaring constant variables:

  const int maxValue = 100;
  

• Declaring pointers to constants (data cannot be changed through the pointer):

  const int* ptr = &maxValue; // cannot change *ptr
  

• Declaring constant pointers (the address cannot be changed):

  int* const ptr = &someVar; // cannot change ptr
  

• Using in function parameters to protect passed data from modification:

  void printValue(const int& value) {
      // value cannot be modified inside the function
      std::cout << value;
  }
  

Thus, const serves to document intentions and prevent errors related to data modification.