/in/foo.c:1:1: warning: return type defaults to 'int' [-Wimplicit-int]
 main(){
 ^~~~
/in/foo.c: In function 'main':
/in/foo.c:3:3: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
   scanf("%d%d",&a,&b);
   ^~~~~
/in/foo.c:3:3: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:3:3: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:4:3: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   printf("%d",a+b);
   ^~~~~~
/in/foo.c:4:3: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:4:3: note: include '<stdio.h>' or provide a declaration of 'printf'