/in/foo.c: In function 'main':
/in/foo.c:4:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%d%d%d",&a,&b,&c);
  ^~~~~
/in/foo.c:4:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:4:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:7:4: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    printf("%d %d",b,a);
    ^~~~~~
/in/foo.c:7:4: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:7:4: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:10:5: warning: incompatible implicit declaration of built-in function 'printf'
     printf("%d %d",c,a);
     ^~~~~~
/in/foo.c:10:5: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:12:5: warning: incompatible implicit declaration of built-in function 'printf'
     printf("%d %d",a,c);
     ^~~~~~
/in/foo.c:12:5: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:15:4: warning: incompatible implicit declaration of built-in function 'printf'
    printf("%d %d",a,b);
    ^~~~~~
/in/foo.c:15:4: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:18:5: warning: incompatible implicit declaration of built-in function 'printf'
     printf("%d %d",c,b);
     ^~~~~~
/in/foo.c:18:5: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:20:5: warning: incompatible implicit declaration of built-in function 'printf'
     printf("%d %d",b,c);
     ^~~~~~
/in/foo.c:20:5: note: include '<stdio.h>' or provide a declaration of 'printf'