how to create and save more than 10^18 Integer Data Type?

hi
i am new to c programming so.
unsigned long long data type have max range up to 18446744073709551615

Code:

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unsigned long long ll = 18446744073709551615;

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how can i create integer data type to save more than 10^18 value ?
thx

The GNU MP Bignum Library

If you don't need more than 128 bits there are native 128-bit values available on 64-bit machines. The maximum for an unsigned 128-bit value is 340282366920938463463374607431768211455, which is about 3.4 * 10^38.
In gcc and clang the type is called __int128 for signed and unsigned __int128 for unsigned.

Code:

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#include <stdio.h>
 
const char *to_str(unsigned __int128 n)
{
    static char buf[40];
    int i = sizeof buf;
    buf[--i] = '\0';
    for ( ; n >= 10; n /= 10) buf[--i] = '0' + (int)(n % 10);
    buf[--i] = '0' + (int)(n % 10);
    return &buf[i];
}
 
unsigned __int128 from_str(const char *s)
{
    unsigned __int128 n = 0;
    for ( ; *s; ++s) n = (n * 10) + (*s - '0');
    return n;
}
 
int main()
{
    // No 128-bit constants available, so if you want to load it
    // with a value larger than 64 bits you need to use a string.
    const char *value = "123456789012345678901234567890123456789";
 
    // No predefined I/O routines for __int128, either.
    unsigned __int128 n = from_str(value);
    n *= 2;
    printf("%s\n", to_str(n));
 
    return 0;
}

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