Need to specify the PATH in C

I using the system command to run an executable file.
for that I need to specify path for the input file and then the output file.
Right now I'm specifying the path manually i.e. the path according to my system. But I need to provide this to the professor when he tries to run it. He uses a location so. Can you suggest me what exactly can I do for specifying dynamic path in C

Code:

---

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

#define PROGNAME "okay"

int main(int argc, const char *argv[]) {
        char *path;
        if (argc < 2) {
                puts("Argument required.");
                return -1;
        }

        path = malloc(strlen(argv[1]) + strlen(PROGNAME) + 1);

        sprintf(path, "%s/%s", PROGNAME, argv[1]);
        puts(path);

        free(path);
        return 0;
}

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> for that I need to specify path for the input file and then the output file.
So what's wrong with
./myprog.exe /here/is/input.txt /there/goes/output.txt


And MK27's malloc is off by 1