Integer constant

Allows values of integer type to be used in expressions directly.

# Notes

Letters in the integer constants are case-insensitive: 0xDeAdBaBeU and 0XdeadBABEu represent the same number(one exception is the long-long-suffix, which is either ll or LL, never lL or Ll)(since C99).

There are no negative integer constants. Expressions such as -1 apply the unary minus operator to the value represented by the constant.

When used in a controlling expression of #if or #elif, all signed integer constants act as if they have type intmax_t and all unsigned integer constants act as if they have type uintmax_t.

Integer constants may be used in integer constant expressions.

Due to maximal munch, hexadecimal integer constants ending in e and E, when followed by the operators + or -, must be separated from the operator with whitespace or parentheses in the source:

Otherwise, a single invalid preprocessing number token is formed, which causes further analysis to fail.

# Example

#include <inttypes.h>
#include <stdio.h>
 
int main(void)
{
    printf("123 = %d\n", 123);
    printf("0123 = %d\n", 0123);
    printf("0x123 = %d\n", 0x123);
    printf("12345678901234567890ull = %llu\n", 12345678901234567890ull);
    // the type is a 64-bit type (unsigned long long or possibly unsigned long)
    // even without a long suffix
    printf("12345678901234567890u = %"PRIu64"\n", 12345678901234567890u );
 
    // printf("%lld\n", -9223372036854775808); // Error:
        // the value 9223372036854775808 cannot fit in signed long long, which
        // is the biggest type allowed for unsuffixed decimal integer constant
 
    printf("%llu\n", -9223372036854775808ull );
    // unary minus applied to unsigned value subtracts it from 2^64,
    // this gives unsigned 9223372036854775808
 
    printf("%lld\n", -9223372036854775807ll - 1);
    // correct way to form signed value -9223372036854775808
}

# See also

C++ documentation