how to generate expected value in C

I am new to the C language and I'm trying to write a simple self banking console program. I want to make a function to generate an account number so I wrote the code below:

int first = 7856123490;
int accountNumber;

int generateAccNo ()
{
    printf("%d", first);
    first = first + 1;
    accountNumber = first;
    return (accountNumber);
}

The whole idea here is that when I call this function, it will get the value in variable called first and add 1 to it and replace the value of first and return that value as accountNumber.

As I expect the first time this function runs it should return 7856123491 this value and the second time it should return 7856123492. So how can I do that?

A more portable solution: use fixed-length type in the <inttypes.h>.

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

int64_t first = 7856123490;
int64_t accountNumber;

int64_t generateAccNo() {
  first = first + 1;
  accountNumber = first;
  return (accountNumber);
}

#define TEST_CNT 10
int main(int argc, char **argv) {
  for (int64_t i = 0; i < TEST_CNT; ++i) {
    int64_t res = generateAccNo();
    printf("%" PRId64 " %016" PRIX64 "\n", res, (uint64_t) res);
  }

  return 0;
}