じゃあ、こうか。
long ch = 0;
char fn[256];
int in;
FILE *fp;
printf("INPUT FILENAME>>");scanf("%s",fn);
if ((fp = fopen(fn, "r")) != NULL) {
while ((in = getc(fp)) != EOF) if(isalnum(in)) ch++;
printf("数字、文字の個数=%ld\n",ch);
fclose(fp);
}
return 0;