What is the correct way to declare and use a FILE * pointer in C/C++? Should it be declared global or local? Can somebody show a good example?

It doesn't matter at all whether it's local or global. The scope of the file pointer has nothing to do with its use.

In general, it's a good idea to avoid global variables as much as possible.

Here's a sample showing how to copy from input.txt to output.txt:

#include <stdio.h>
int main (void) {
    FILE *fin;
    FILE *fout;
    int c;

    fin = fopen ("input.txt", "r");
    if (fin != NULL) {
        fout = fopen ("output.txt", "w");
        if (fout != NULL) {
            c = fgetc (fin);
            while (c >= 0) {
                fputc (c, fout);
                c = fgetc (fin);
            }
            fclose (fout);
        } else {
            fprintf (stderr, "Cannot write to output.txt");
        }
        fclose (fin);
    } else {
        fprintf (stderr, "Cannot read from input.txt");
    }
    return 0;
}

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