What is the effect of using the `const` keyword in variable declarations?

Using the const keyword in variable declarations is essential in C programming because it signifies that the variable's value is constant after its initial assignment. When a variable is declared with const, any attempt to modify its value later in the program results in a compilation error. This feature helps enforce immutability, making the code safer and easier to understand, as it communicates to other programmers that this variable should not change throughout its scope.

Furthermore, this can help prevent unintended side effects of modifying data that should remain constant, which is particularly important in functions that are meant to work with fixed data. Code that uses const can also become more efficient, as the compiler can make optimizations knowing certain values won't change.

The other options do not accurately describe the function of const. For example, it does not allow a variable to change its value, define any special type, or convert a variable into a pointer. The core role of const is to protect the variable from modification, which is why it is crucial for maintaining data integrity within a program.