/in/foo.c:1:1: warning: data definition has no type or storage class
    1 | s = input()
      | ^
/in/foo.c:1:1: warning: type defaults to 'int' in declaration of 's' [-Wimplicit-int]
/in/foo.c:1:5: warning: implicit declaration of function 'input' [-Wimplicit-function-declaration]
    1 | s = input()
      |     ^~~~~
/in/foo.c:1:5: error: initializer element is not constant
/in/foo.c:2:1: error: expected ',' or ';' before 'upper'
    2 | upper = 0
      | ^~~~~