<limits.h> tells you the range of the built-in types on this platform; <stdint.h> gives you types with an exact width when you need one.

limits.h and float.h

C

#include <stdio.h>
#include <limits.h>
#include <float.h>

int main(void) {
    printf("CHAR_BIT  = %d\n", CHAR_BIT);
    printf("SCHAR     = %d .. %d\n", SCHAR_MIN, SCHAR_MAX);
    printf("UCHAR_MAX = %d\n", UCHAR_MAX);
    printf("SHRT      = %d .. %d\n", SHRT_MIN, SHRT_MAX);
    printf("INT       = %d .. %d\n", INT_MIN, INT_MAX);
    printf("UINT_MAX  = %u\n", UINT_MAX);
    printf("LLONG_MAX = %lld\n", LLONG_MAX);
    printf("DBL_MAX   = %g, DBL_EPSILON = %g\n", DBL_MAX, DBL_EPSILON);
    return 0;
}

Output

CHAR_BIT  = 8
SCHAR     = -128 .. 127
UCHAR_MAX = 255
SHRT      = -32768 .. 32767
INT       = -2147483648 .. 2147483647
UINT_MAX  = 4294967295
LLONG_MAX = 9223372036854775807
DBL_MAX   = 1.79769e+308, DBL_EPSILON = 2.22045e-16

stdint.h — exact, least and fast types

Type	Meaning
`int8_t`, `int16_t`, `int32_t`, `int64_t`	Exactly N bits, two’s complement (optional but universally available)
`uint8_t` … `uint64_t`	Unsigned exact-width
`int_least16_t`	Smallest type with at least 16 bits
`int_fast32_t`	Fastest type with at least 32 bits
`intmax_t` / `uintmax_t`	Widest integer type
`intptr_t` / `uintptr_t`	Integer that can hold a pointer value
`size_t` (`<stddef.h>`)	Unsigned result of `sizeof`; use for sizes and indexes
`ptrdiff_t` (`<stddef.h>`)	Signed difference of two pointers

Printing them portably: inttypes.h

C

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>

int main(void) {
    int64_t big = INT64_MAX;
    uint8_t small = UINT8_MAX;
    uint32_t mask = 0xDEADBEEF;
    printf("big   = %" PRId64 "\n", big);
    printf("small = %" PRIu8 "\n", small);
    printf("mask  = 0x%" PRIX32 "\n", mask);
    printf("sizes = %zu %zu %zu\n", sizeof(int8_t), sizeof(int32_t), sizeof(uint64_t));
    return 0;
}

Output

big   = 9223372036854775807
small = 255
mask  = 0xDEADBEEF
sizes = 1 4 8

When should you use int vs int32_t?

What is size_t and why is it unsigned?