/in/foo.c: In function 'main':
/in/foo.c:36:12: warning: implicit declaration of function 'strlen' [-Wimplicit-function-declaration]
   36 |     len1 = strlen(M);
      |            ^~~~~~
/in/foo.c:2:1: note: include '<string.h>' or provide a declaration of 'strlen'
    1 | #include<stdio.h>
  +++ |+#include <string.h>
    2 | int N;
/in/foo.c:36:12: warning: incompatible implicit declaration of built-in function 'strlen' [-Wbuiltin-declaration-mismatch]
   36 |     len1 = strlen(M);
      |            ^~~~~~
/in/foo.c:36:12: note: include '<string.h>' or provide a declaration of 'strlen'