how to handle big number here

Question

#include<stdio.h>
#include<stdlib.h>
int main()
{
    long long int n;
    char c[200];
    scanf("%lld",&n);
    itoa(n*n*n*n,c,10);
    printf("%s",c);

}

input: 90625

output: -1726117887

basically, my code is calculating n^4 and converting it into a string. but the problem is I am not able to do so for bigger numbers. please resolve my issue.

67451572418212890625 is too big to fit in a 64-bit int. You need [bignums](https://stackoverflow.com/questions/45527972/big-numbers-in-c). — tadman, Mar 20 '21 at 05:45
The `itoa()` call is completely pointless here. You're using `printf` which already has this conversion capability: `printf("%lld", n*n*n*n)` — tadman, Mar 20 '21 at 05:46
It's not possible in this way, it won't fit in a long long int, better is to make a char[200] and fill it manually. You can do a loop for three times multiplication each time taking an input as a char[] and a long long int and returning a char[]. — TheSYNcoder, Mar 20 '21 at 05:48
Consider using libraries like http://gmplib.org/ but be aware that C is not the same as C++. Read [n1570](http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf) -or a newer C standard- and [n3337](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3337.pdf) or a newer C++ standard. See [this website](https://en.cppreference.com/w/) — Basile Starynkevitch, Mar 20 '21 at 05:59
Calculate `4*log(90625)/log(2)` (in any base of logarithms) and the result is about `65.9`. That means you need a minimum of a 66 bit integral type to be able to represent `90625` to the fourth power. A `long long int` is only guaranteed to be (no smaller than) a 64-bit type, and includes a sign bit, so cannot represent a value that needs to be represented using a 66-bit type. You'll need to find (or roll your own) a library to handle such values. Incidentally, `n*n*n*n` can be done with exactly two multiplications (no need for 4) if you use a type that can represent sufficiently large values — Peter, Mar 20 '21 at 06:05

score 2 · Answer 1 · answered Mar 20 '21 at 05:54

There are many problems:

itoa is for integer, you are trying to call a function that returns an integer with a value that exceeds (overflow) INT_MAX, as (90625^4) is way bigger than the maximum value that can fit into an int.
If you check the value of unsigned long long, 18446744073709551615, you will see that you are short of only one more power of 10 (0.27348130536 if divided by 90625^4). Your best bet is to use a library that can handle such number, you can use the one suggested by tadman: big num

how to handle big number here

1 Answers1