/in/foo.c: In function 'add':
/in/foo.c:10:17: error: 'str' undeclared (first use in this function)
   10 |             if (str[j] > str[j + 1])
      |                 ^~~
/in/foo.c:10:17: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c: In function 'main':
/in/foo.c:25:30: error: 'a' undeclared (first use in this function)
   25 |                  scanf("%c",&a[i]);
      |                              ^
/in/foo.c:27:9: warning: unused variable 'n' [-Wunused-variable]
   27 |     int n= strlen(a);
      |         ^
/in/foo.c:22:10: warning: unused variable 'str' [-Wunused-variable]
   22 |     char str[100];
      |          ^~~