File contents falsification with bitwise operation in C

I have this little program which reads a long text document from allomany.txt.It contains a long text where we have some numbers.Now I need to falsify every number: Let is assume the program needs to read the text from file and I need to find a number(the number is string).Then I need to check if the string is a number. If yes then I need to falsify it by using bitwise operations.

Falsification: if I find a number in string(atoi, sscanf) then I need to increment the number which is found in the string. Example: if the program finds 14 we increase it 15 using bitwise operations. I found an example for this on the net if I remember correctly: (-(~n)). If I don't use bitwise operations it works.

The question: how to do this with bitwise operations ?

#include <stdio.h>
#include <stdlib.h>

int main()
{
    FILE *fin,*fout;
    char *token, s[1000];

    fin = fopen("allomany.txt","rt");
    fout = fopen("hamisitott.txt","wt");

    while (fscanf(fin, "%[^\n]\n", s) != EOF) {
        token = strtok(s, " ");
        while (token != NULL) {
            if (atof(token) > 0)
                fprintf(fout, "%g ", atof(token) + 1);
            else fprintf(fout, "%s ", token);
            token = strtok(NULL, " ");
        }
        fprintf(fout, "\n");
    }

    fclose(fin);
    fclose(fout);

    return EXIT_SUCCESS;
}

Solution

Incrementing the numbers with bitwise operations seems a bit complicated, I suggest a simple alternative: change every digit in the file from even to odd and vice versa by flipping the low order bit:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    FILE *fin = fopen("allomany.txt", "r");
    FILE *fout = fopen("hamisitott.txt", "w");
    int c;

    if (fin == NULL || fout == NULL) {
        fprintf(stderr, "cannot open files\n");
        exit(EXIT_FAILURE);
    }
    while ((c = getc(fin)) != EOF) {
        if (c >= '0' && c <= '9')
            c = '0' + ((c - '0') ^ 1);
        putc(c, fout);
    }
    fclose(fin);
    fclose(fout);

    return EXIT_SUCCESS;
}

You could also implement other permutations of digits with a different expression (but without bitwise operations):

c = "9876543210"[c - '0'];

EDIT I changed c ^= 1 into c = '0' + ((c - '0') ^ 1) to avoid assuming that '0' be even. The C Standard only guarantees that digits '0' through '9' are adjacent and strictly positive.