Data Types in C Programming

Introduction

Every variable in C has a data type that tells the compiler how much memory to allocate and what operations are allowed. C provides several fundamental types and lets you build complex types from them (arrays, structures, pointers).

Fundamental Data Types

Use sizeof(type) to check actual sizes on your system:

#include <stdio.h>

int main(void) {
    printf("char:   %zu byte(s)\n", sizeof(char));
    printf("int:    %zu byte(s)\n", sizeof(int));
    printf("float:  %zu byte(s)\n", sizeof(float));
    printf("double: %zu byte(s)\n", sizeof(double));
    return 0;
}

Sample Output (typical 64-bit system)

char:   1 byte(s)
int:    4 byte(s)
float:  4 byte(s)
double: 8 byte(s)

Type Modifiers

C extends basic types with modifiers:

unsigned int count = 100;
short int age = 25;
long int bigNumber = 1000000L;

Format Specifiers for printf

Example — Declaring and Printing Values

#include <stdio.h>

int main(void) {
    int age = 20;
    float height = 5.9f;
    char grade = 'A';

    printf("Age:    %d years\n", age);
    printf("Height: %.1f feet\n", height);
    printf("Grade:  %c\n", grade);
    return 0;
}

Sample Output

Age:    20 years
Height: 5.9 feet
Grade:  A

Best Practices

• Choose the smallest type that fits your data to save memory.
• Use double instead of float unless you have a specific reason.
• Append f to float literals (3.14f) to avoid unintended double promotion.
• Always match format specifiers to the actual variable type.

Common Mistakes

• Using %d to print a float — causes undefined behaviour; use %f.
• Assuming fixed sizes — always use sizeof or <stdint.h> types (int32_t) for portability.

Related Pages

Continue learning with these related tutorials and programs:

• C Tutorials — Browse all C Tutorials.
• C Introduction — Start here — what C is and why it matters.
• Command Line Arguments in C (argc and argv) — More in c basics.
• C History — More in c basics.