写一段程序C语言实现读取记事本中字母后面的数字

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

int main() {
FILE *fp;
char filename[100], ch;
int num;

printf("请输入要读取的记事本文件名：");
scanf("%s", filename);

fp = fopen(filename, "r");

if (fp == NULL) {
printf("无法打开文件！\n");
exit(1);
}

while ((ch = fgetc(fp)) != EOF) {
if (ch >= 'a' && ch <= 'z') {
ch = fgetc(fp);
if (ch >= '' && ch <= '9') {
num = ch - '';
printf("%d ", num);
}
}
}

fclose(fp);

return ;
}