foo.c:1:1: warning: return type defaults to 'int' [-Wimplicit-int]
    1 | main(a,b){scanf("%d%d",&a,&b);printf("%d",a+b);}
      | ^~~~
foo.c: In function 'main':
foo.c:1:1: warning: type of 'a' defaults to 'int' [-Wimplicit-int]
foo.c:1:1: warning: type of 'b' defaults to 'int' [-Wimplicit-int]
foo.c:1:11: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | main(a,b){scanf("%d%d",&a,&b);printf("%d",a+b);}
      |           ^~~~~
foo.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | main(a,b){scanf("%d%d",&a,&b);printf("%d",a+b);}
foo.c:1:11: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    1 | main(a,b){scanf("%d%d",&a,&b);printf("%d",a+b);}
      |           ^~~~~
foo.c:1:11: note: include '<stdio.h>' or provide a declaration of 'scanf'
foo.c:1:31: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    1 | main(a,b){scanf("%d%d",&a,&b);printf("%d",a+b);}
      |                               ^~~~~~
foo.c:1:31: note: include '<stdio.h>' or provide a declaration of 'printf'
foo.c:1:31: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
foo.c:1:31: note: include '<stdio.h>' or provide a declaration of 'printf'