What are Data Types in C?

In the C programming language, a data type defines the type and size of data associated with variables and function return values.

Because C is a statically typed language, every variable must have an explicit type declaration so the compiler can allocate the exact amount of stack or heap memory.

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1. Basic Primitive Types Overview

The standard C language provides four fundamental primitive data types:

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2. Type Modifiers (Short, Long, Signed, Unsigned)

You can alter the storage range and signedness of primitive types using modifier keywords:

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>
#include <limits.h>

int main() {
    short int smallNumber = 32767;
    unsigned int positiveOnly = 4000000000U;
    long long bigInt = 9223372036854775807LL;

    printf("Short int: %d (Size: %zu bytes)\n", smallNumber, sizeof(smallNumber));
    printf("Unsigned int: %u (Size: %zu bytes)\n", positiveOnly, sizeof(positiveOnly));
    printf("Long long: %lld (Size: %zu bytes)\n", bigInt, sizeof(bigInt));

    return 0;
}

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3. Fixed-Width Integer Types (<stdint.h>)

For cross-platform systems programming and embedded systems, ISO C99 introduced exact-width integer definitions in <stdint.h>:

• int8_t / uint8_t: Exactly 8 bits.
• int16_t / uint16_t: Exactly 16 bits.
• int32_t / uint32_t: Exactly 32 bits.
• int64_t / uint64_t: Exactly 64 bits.

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>
#include <stdint.h>

int main() {
    uint32_t packetId = 0xAABBCCDD;
    printf("Fixed-width 32-bit integer: 0x%X\n", packetId);
    return 0;
}

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4. Modern Boolean Type (bool in C23)

In C23, bool, true, and false are native language keywords. In older C99/C11 standards, including <stdbool.h> provides identical behavior.

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Related References & Guides

• Look up formatted input and output tokens in C Format Specifiers Reference.
• Review mathematical and comparison operations in the C Operators Reference.
• Test variable memory limits in the Online C Compiler.