foo.c: In function 'main':
foo.c:9:3: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
   scanf("%s",s);
   ^~~~~
foo.c:9:3: warning: incompatible implicit declaration of built-in function 'scanf'
foo.c:9:3: note: include '<stdio.h>' or provide a declaration of 'scanf'
foo.c:20:5: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
     printf("no");
     ^~~~~~
foo.c:20:5: warning: incompatible implicit declaration of built-in function 'printf'
foo.c:20:5: note: include '<stdio.h>' or provide a declaration of 'printf'
foo.c:22:5: warning: incompatible implicit declaration of built-in function 'printf'
     printf("yes");
     ^~~~~~
foo.c:22:5: note: include '<stdio.h>' or provide a declaration of 'printf'
foo.c:6:17: warning: unused variable 'p' [-Wunused-variable]
   int n,i=0,sum,p;
                 ^

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