Variable facts for kids
A variable is like a placeholder for an amount or value that can change. Think of it as an empty box where you can put different numbers or information. The opposite of a variable is a constant, which is a value that always stays the same, like the number 5.
Variables in Math
In mathematics, we often use letters to represent variables. This helps us solve problems where we don't know the exact number yet. For example, you might see letters like x or y in an equation.
Here are some common letters and what they often stand for:
- The letters m, n, p, q are often used for whole numbers.
- The letters a, b, c are often used for numbers that multiply other variables in functions.
- The letters i, j, k are often used to count things in a list.
- The letter t is often used to represent time.
- The letter z is often used for complex numbers, which are a special type of number.
Most letters in equations show numbers that are unknown. One exception is e, which is a constant number, not a variable. Using a type of math called algebra, we can find the value of these unknown variables.
A regular number always keeps its value. For example, the number 7 is always 7. This is true for all types of numbers, whether they are fractions (like 1/2), never-ending decimals (like the square root of 2), real numbers (like 
), or imaginary numbers (like 
).
Variables are also used a lot in science. They usually represent things that can change. For example, if you stand 5 feet away from a building, your distance from the building is a fixed amount. It doesn't change over time. But if you start walking away from the building, your distance from it is now a variable. It changes as you walk. So, you can't use just one number for it, because it might be 1 foot now and 2 feet a second later.
Variables in Computer Science
In computer science, a variable is a value in a program that can change while the program is running. It doesn't have to be a number. A variable can store many different kinds of information, such as:
- A string (which is text, like a name or a sentence).
- A date.
- An amount of money.
- An object like a picture.
- Or even nothing at all (this is called null).
The value stored in a variable can change how a program works. Because of this, variables are often used to store information that a user types in (called input) or information that the program shows to the user (called output).
Different programming languages handle variables in slightly different ways. Most languages let you use almost any text as the name for a variable, as long as it's not a special "reserved" word that the language uses for something else. It's a good idea in computer programming to give variables names that tell you what they store. For example, names like "person", "age", or "total" are very helpful.
Some languages, like C and Java, require you to tell the program what kind of data the variable will hold (like a number or text) when you first create it. This is called "declaring" the data type. Other languages, like Python and Visual Basic, are more flexible. They don't require you to declare the type, and the type of information a variable holds can even change if you store a new kind of value in it.
Related pages
See also
In Spanish: Variable para niños
