Understanding C Data Types: Categories, Sizes, and Examples

Primary Data Type #1: int — The Workhorse

intstoreswhole numbers— no decimal points, no fractions.

Memory size:typically4 bytes(32 bits) on modern systemsRange:roughly−2.1 billion to +2.1 billion

The int Family: Size Modifiers

C lets you resize integers with modifiers:

And each comes in anunsignedflavor — trade away negatives, double your positive range:

unsigned charmaxing out at exactly255is why colors on your screen run from 0–255. That's not a coincidence — that's a data type showing up in your daily life.

Primary Data Type #2: float and double — The Decimal Duo

For numbers with fractional parts, C offers two precisions:

⚠️The famous floating-point surprise:

Computers store decimals in binary, and some fractions (like 0.1) can't be represented exactly — just like ⅓ can't be written exactly in decimal. This affectseverylanguage, but C shows it to you honestly.Practical rule:usedoubleby default, and never compare floats with==.

Primary Data Type #3: char — Small but Mighty

charstores asingle character— one byte, holding values from −128 to 127 (or 0 to 255 unsigned).

But here's the secret that unlocks a dozen "aha" moments:a char is really a small integer wearing a costume.'A'is the number65underneath (its ASCII code), which means this genuinely works:

That last line — adding 1 to'A'to get'B'— is why C programmers can loop through the alphabet as easily as through numbers.

Primary Data Type #4: void — The Deliberate Nothing

voidmeans"no value here"— and it appears in two places:

You'll also meetvoid*later — a "pointer to anything" — when you reach dynamic memory. For now, remember:voidis C's way of saying "empty on purpose."

The Complete Sizes & Ranges Reference Table

Bookmark this — it's the table every C programmer memorizes eventually:

⚠️Important honesty note:C doesnotguarantee exact sizes — it guaranteesminimums. Anintis "at least 2 bytes," which is why old systems had 2-byte ints. Which raises the question: how do you know the size onyourmachine?

Ask Your Compiler: The sizeof Operator

C gives you a built-in detective —sizeof— that reports exactly how many bytes any type occupies onyoursystem:

Output on a typical modern system:

Run this on your own machine — the answers are your system's truth. (Fun fact:sizeofis a compile-timeoperator, not a function. One of the few keywords that does real work.)

#include <stdio.h>
#include <limits.h>
int main() {
    int max = INT_MAX;
    // 2147483647
    printf("Max:     %d\n", max);
    printf("Max + 1: %d\n", max + 1);
    // -2147483648 — overflowed!
    return 0;
}