Convert From Unicode Signature (BOM) to Unicode

#include <windows.h>
#include <stdio.h>

int main(int argn, char * argv[]) {
    FILE *fp;

    if (argn < 2) {
        MessageBox(0, "Where is second argument?", "PVH", 0);
        return 0;
    }
    int iFile;
    for (iFile = 1; iFile < argn; iFile++) {
        fp = fopen(argv[iFile], "r");
        if (!fp) {
            MessageBox(0, "Read file failed", "PVH", 0);
            continue;
        }
    
        char szString[65535];
        int nRead = fread(szString, sizeof(char), 65535, fp);
        //printf("%d ", nRead);
        int iStart = 0;
        int iFinish = nRead;
        if(szString[0] == -17 && szString[1]==-69 && szString[2]==-65) {
            printf("BOM will be removed");
            iStart = 3;
        }
        rewind(fp);
        fclose(fp);
        if (iStart == 0) continue;
        fp = fopen(argv[iFile], "w+"); int i;
        for (i = iStart; i < iFinish; i++) {
            fputc(szString[i], fp);
        }
        fclose(fp);
    }
    return 1;
}