/in/foo.c: In function 'main':
/in/foo.c:5:1: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
 scanf("%d",&a);
 ^~~~~
/in/foo.c:5:1: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:5:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:11:1: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
 printf("%d\n",sum);
 ^~~~~~
/in/foo.c:11:1: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:11:1: note: include '<stdio.h>' or provide a declaration of 'printf'