Understanding C Data Types: With Syntax, Examples & Outputs

When you write code in C, you work with data—numbers, characters, decimal values, and so on. But the computer doesn’t automatically know what kind of data you're using. That’s why we use data types. They help tell the compiler: “This variable is going to store an integer,” or “This one holds a letter.” Without this clarity, the program would be confused about how much space to reserve in memory or how to work with the variable.

What Are Data Types in C?

A data type defines the kind of data a variable can store—like an integer, a floating-point number, or a single letter. In C, you must declare the type of a variable before using it. This helps the compiler handle the data properly and prevents unexpected errors.

Why Do We Use Data Types?

Imagine you're building an inventory management system. For each product, you need to store:
Product ID → a whole number
Product Name → a set of characters (a string)
Product Price → a decimal number
Now, if you accidentally try to store a product name in a variable that was meant for numbers, your program won't work correctly. That’s exactly why data types are necessary. They help with:

• Correct Data Storage: Each variable holds exactly the kind of value it's meant to.
• Efficient Memory Usage: Different data types use different amounts of memory.
• Error Checking: The compiler will show an error if you try to do something incorrect with the data.
• Better Code Clarity: Other developers (or even you later) can quickly understand what each variable is used for.

Types of Data Types in C

C has three main categories:

• Primitive Data Types: The basic types like numbers (int, float, double), characters (char), and true/falsevalues (_Bool).
• Derived Data Types: Built from basic types, like lists (arrays), references (pointers), and functions.
• User-Defined Data Types: Custom types created by programmers, like groups of variables (struct), sets of constants (enum), and new names for types (typedef).

Primitive Data Types

The size of each data type (e.g., int, float, double, long) can vary depending on the compiler and system architecture (e.g., 32-bit or 64-bit).

To Check Size of Each Data Type

Syntax:

sizeof(dataType)

Example:

#include <stdio.h>
    int main() {
        printf("Size of int: %zu bytes\n", sizeof(int));
        printf("Size of float: %zu bytes\n", sizeof(float));
        printf("Size of double: %zu bytes\n", sizeof(double));
        printf("Size of char: %zu bytes\n", sizeof(char));
        printf("Size of long: %zu bytes\n", sizeof(long));
        return 0;
    }

Sample Output (may vary):
Size of int: 4 bytes
Size of float: 4 bytes
Size of double: 8 bytes
Size of char: 1 byte
Size of long: 8 bytes

int

The most commonly used integer data type. Represents whole numbers(like 1, -5, 42).

Syntax:

int variableName = value;

Size & Range: Typically 4 bytes and -2,147,483,648 to 2,147,483,647

Example:

#include <stdio.h>

    int main() {
        int productId = 344334;
        printf("%d\n", productId);
        return 0;
    }

Output: 344334

float

A single-precision floating point number used for decimal values. It’s useful when you need to represent approximate decimal values.

Syntax:

float variableName = value;

Size & Range: Typically 4 bytes and ±3.4e−38 to ±3.4e+38

Example:

#include <stdio.h>

    int main() {
        float productPrice = 99.36f;
        printf("%.1f\n", productPrice);
        return 0;
    }

Output: 99.36

double

A double-precision floating point number for more precise decimal values.

Syntax:

double variableName = value;

Size & Range: Typically 8 bytes and ±1.7e−308 to ±1.7e+308

Example:

#include <stdio.h>

    int main() {
        double distance = 9.346899;
        printf("%lf\n", distance);
        return 0;
    }

Output: 9.346899

char

Represents a single character. It’s useful for making decisions in programs based on conditions.

Syntax:

char variableName = 'A';

Size & Range: 1 byte and typically 0 to 255

Example:

#include <stdio.h>

    int main() {
        char response = 'Y';
        printf("%c\n", response);
        return 0;
    }

Output: Y

_Bool

Represents boolean values (true/false) in C.

Syntax:

_Bool variableName = 1; // 1 for true, 0 for false

Example:

#include <stdio.h>
    #include <stdbool.h>

    int main() {
        bool batteryLow = true;
        printf("%d\n", batteryLow);
        return 0;
    }

Output: 1

void

Indicates the absence of a value. Commonly used for functions that do not return any result or to represent a placeholder.

Official C Documentation: C Data Types Reference

Common Errors in C

Here are some common beginner mistakes when working with different data types in C. Watch out for these to avoid unexpected behavior!

int

Declaring a variable without specifying its type:

productId = 1234; // Error: type not specified

float

Forgetting to add 'f' at the end of a float literal:

float temperature = 98.6; // Implicit conversion from double

Mixing up float and double format specifiers in printf():

printf("%lf", temperature); // Works but %f is standard

double

Using %f instead of %lf in scanf():

double value; scanf("%f", &value); // Error: %f reads float

In printf(), %f and %lf both work for double:

printf("%f", value); // or printf("%lf", value);

char

Trying to assign multiple characters to a char variable:

char letter = 'AB'; // Error: char can store only one character

_Bool

Forgetting to include <stdbool.h> when using bool:

bool flag = true; // Error: 'bool' undeclared

Using %d with bool in printf() but expecting true/false:

printf("%d", flag); // Outputs 1 or 0

void

Trying to declare a variable of type void:

void result; // Error: void is not a variable type

Remember: Always double-check your variable types and format specifiers when working with C. Small mistakes can cause big issues!

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