1 #include <stdio.h>
 2 int main(int argc,char **argv){
 3     FILE *r=fopen(argv[1],"r");
 4     FILE *w=fopen(argv[2],"w");
 5     char t;
 6     int cnt,s=0;
 7     while((t=fgetc(r))!=EOF){
 8         if(t>=‘0‘&&t<=‘9‘){
 9             fputc(t,w);
10             s=1;
11         }else {
12             if(s==1){
13                 fputc(‘\n‘,w);
14                 s=0;
15             }
16         }
17     }
18     return 0;
19 }

 1 #include <stdio.h>
 2 #include <string.h>
 3 int main(int argc,char **argv){
 4     FILE *r=fopen(argv[1],"r");
 5     FILE *w=fopen(argv[2],"w");
 6     char buff[10000];
 7     while(NULL!=fgets(buff,10000,r)){
 8         if(strlen(buff)==5){
 9             fputs(buff,w);
10         }
11     }
12     return 0;
13 }

 1 #include <stdio.h>
 2 #include <string.h>
 3 int main(int argc,char **argv){
 4     int cnt=0;
 5     int i,j;
 6     char list[10000][10];
 7     FILE *r1=fopen(argv[1],"r");
 8     FILE *r2=fopen(argv[2],"r");
 9     FILE *w=fopen(argv[3],"w");
10     char buff[10];
11     while(NULL!=fgets(buff,10,r1)){
12         strcpy(list[cnt++],buff);
13     }
14     while(NULL!=fgets(buff,10,r2)){
15         int s=0;
16         for(i=0;i<cnt;++i){
17             if(strcmp(list[i],buff)==0){
18                 s=1;
19                 break;
20             }
21         }
22         if(s==0){
23             fputs(buff,w);
24         }
25     }
26     return 0;
27 }