C Constants

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Constants

If you don't want others (or yourself) to change existing variable values, you can use the const keyword.

This will declare the variable as "constant", which means unchangeable and read-only:

Example

const int myNum = 15; // myNum will always be 15
myNum = 10; // error: assignment of read-only variable 'myNum'

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You should always declare the variable as constant when you have values that are unlikely to change:

Example

const int minutesPerHour = 60;
const float PI = 3.14;

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Notes On Constants

When you declare a constant variable, it must be assigned with a value:

Example

Like this:

const int minutesPerHour = 60;

This however, will not work:

const int minutesPerHour;
minutesPerHour = 60; // error

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Good Practice

Another thing about constant variables, is that it is considered good practice to declare them with uppercase. It is not required, but useful for code readability and common for C programmers:

Example

const int BIRTHYEAR = 1980;

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