Basic data types

1. char: Stores character-sized values. It is commonly used for individual characters and character arrays.
2. Integer types: short, int, long and long long store whole numbers. Signed forms can represent negative values; unsigned forms represent non-negative values.
3. Floating types: float, double and long double store approximate values that can include fractions.
4. Boolean type: In C11, _Bool stores logical values as 0 or 1. The stdbool.h header provides the name bool.
5. void: Shows the absence of a value, such as a function that returns no result.

Sizes and ranges

Type sizes can differ between implementations. int is not always two bytes, and long double is not always ten bytes. sizeof reports a size in C bytes. sizeof(char) is always 1. CHAR_BIT, from limits.h, tells us how many bits are in a C byte. INT_MIN and INT_MAX give the int limits. Use %zu to print a sizeof result, whose type is size_t.

Enumeration

An enumeration gives names to related integer values. In enum Day { MONDAY, TUESDAY, WEDNESDAY };, the values start at 0 unless other values are specified. Thus TUESDAY has value 1. Names can make the code easier to read than unexplained numbers. Do not assume an enum object always occupies one byte.

Choice of type

Use an integer for a count and a floating type when a fractional result is required. Check the largest allowed value and intermediate calculations. Every fixed-width type has a limited range. A floating type does not store every decimal fraction exactly. Plain char can act as signed or unsigned depending on the implementation; specify the form when that difference matters.

Reference table

C program and output

/* CodeBhavya | PPS AR25 | Learning example */
#include <stdio.h>
#include <limits.h>
int main(void)
{
    printf("sizeof(char) = %zu C byte\n", sizeof(char));
    printf("CHAR_BIT is at least 8: %d\n", CHAR_BIT >= 8);
    printf("int supports at least -32767..32767: %d\n",
           INT_MIN <= -32767 && INT_MAX >= 32767);
    return 0;
}

sizeof(char) = 1 C byte
CHAR_BIT is at least 8: 1
int supports at least -32767..32767: 1

Key points

• Use sizeof and limits macros to inspect the implementation.
• A C byte is the unit measured by sizeof.