When learning C programming, one of the first concepts you encounter is data types. They’re the foundation of how all programs work. They define the kind of data a variable can hold, how much memory it occupies, and what operations you can perform on it.

What Are Data Types?

In simple terms, a data type tells the computer what kind of information we’re dealing with. Is it a whole number like 42, a decimal like 3.14, or just a single letter like ‘A’? Each type of data is stored differently inside the computer’s memory, and the data type helps the computer know how to store, read, and process it properly.

C provides several basic data types:

Even though we write our programs in words and numbers, the computer only sees binary — long sequences of 0s and 1s. That’s why the data type is important: it tells the computer how many bits to use and how to interpret them. For example, a char usually uses 1 byte (8 bits), while an int may use 4 bytes (32 bits). Without the correct data type, the computer might completely misinterpret the value.

A small question:

At first, I wondered why computers don’t use our everyday decimal system. After all, we’re used to counting from 0 to 9, not just 0 and 1. But it turns out, binary isn’t just a choice — it’s a necessity. Computer hardware is made of tiny circuits that can only recognize two states: on and off. These two states perfectly match the digits of binary: 1 (on) and 0 (off). Although the long sequences of 0s and 1s may appear unnecessarily lengthy, computers actually have very high processing speeds. Handling binary data is extremely simple for computers.

What I found really interesting is that almost everything in computing — from memory allocation to network protocols — is based on powers of 2. For example, a byte is 8 bits, and many standard sizes (like 256 MB or 1 GB) are all powers of 2. This structure makes it easier for hardware and software to communicate smoothly.

Why Choosing the Right Type Matters

Using the correct data type isn’t just about saving memory. It also helps avoid problems in your program. For instance, if you try to store a decimal value like 7.5 in an int variable, the decimal part will be lost, and you’ll end up with just 7. In more complex programs, such small errors can lead to big problems — especially in calculations.

C is also a strongly typed language. That means you can’t randomly mix and match data types. If you try to assign a float to an int, or a char to a float, the compiler will usually give a warning or error unless you handle it correctly.

A Closer Look at Data Representation

Fixed-Point vs Floating-Point Numbers

· Definitions：Fixed-point: A number without an exponential part. （eg. 10, 2025, -11, etc.）

Floating-Point Numbers: A number whose decimal point position fluctuates due to the existence and different magnitudes of the exponent, that is, a real number.

Internally, floating-point numbers are split into three parts:

The sign (positive or negative)
The exponent (which tells how many places to shift)
The mantissa or significand (which contains the actual digits)

Then, how we express the same floating-point number in everyday scientific notation and C programming syntax?

examples:

In the above examples, we can see that the C notation replaces "×10" with "e" and allows optional signs for the exponent.

How Much Space Does Each Type Use?

Different data types use different amounts of memory depending on the system. Here are some typical sizes on a 32-bit or 64-bit system:

Signed vs Unsigned Types

By default, numeric types in C are signed, which means they can store both positive and negative numbers. But sometimes, you don’t need negative values. In that case, you can use an unsigned type:

unsigned int x = 300;

This allows the variable to use all its bits for positive numbers, which doubles the maximum value it can hold. For example, a regular char can go from -128 to 127, but an unsigned char goes from 0 to 255.

This is useful when you’re sure the values won’t go negative — like when working with memory addresses, pixel values, or counting things.

Why Data Types Matter in C Programming