foo.c:1:8: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token
    1 | include<stdio.h>
      |        ^
foo.c: In function 'fun':
foo.c:17:5: error: expected ',' or ';' before 'for'
   17 |     for (int i=19;i>0;i--)
      |     ^~~
foo.c:17:19: error: 'i' undeclared (first use in this function)
   17 |     for (int i=19;i>0;i--)
      |                   ^
foo.c:17:19: note: each undeclared identifier is reported only once for each function it appears in
foo.c:17:26: error: expected ';' before ')' token
   17 |     for (int i=19;i>0;i--)
      |                          ^
      |                          ;
foo.c:17:26: error: expected statement before ')' token
foo.c:19:29: warning: implicit declaration of function 'chengji' [-Wimplicit-function-declaration]
   19 |          sum=sum+(a[i]-'0')*chengji(2,19-i);
      |                             ^~~~~~~
foo.c: In function 'main':
foo.c:25:4: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   25 |    printf("10010");
      |    ^~~~~~
foo.c:1:1: note: include '<stdio.h>' or provide a declaration of 'printf'
  +++ |+#include <stdio.h>
    1 | include<stdio.h>
foo.c:25:4: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   25 |    printf("10010");
      |    ^~~~~~
foo.c:25:4: note: include '<stdio.h>' or provide a declaration of 'printf'
foo.c:26:4: warning: implicit declaration of function 'gets_s' [-Wimplicit-function-declaration]
   26 |    gets_s(a,21);
      |    ^~~~~~
foo.c: In function 'fun':
foo.c:21:1: warning: control reaches end of non-void function [-Wreturn-type]
   21 | }
      | ^

[Hydro](https://hydro.ac)提供评测服务