/in/foo.c:3:6: warning: conflicting types for built-in function 'abs'
 void abs(char input,char output)
      ^~~
/in/foo.c: In function 'abs':
/in/foo.c:6:19: error: subscripted value is neither array nor pointer nor vector
  for(int i=0;input[i]!=='0';i++)
                   ^
/in/foo.c:6:24: error: expected expression before '=' token
  for(int i=0;input[i]!=='0';i++)
                        ^
/in/foo.c:7:11: error: subscripted value is neither array nor pointer nor vector
   if(input[i]='a'||input[i]='e'||input[i]='i'||input[i]='o'||input[i]='u')
           ^
/in/foo.c:9:10: error: subscripted value is neither array nor pointer nor vector
    output[j++]=input[i];
          ^
/in/foo.c:9:21: error: subscripted value is neither array nor pointer nor vector
    output[j++]=input[i];
                     ^
/in/foo.c: In function 'main':
/in/foo.c:18:6: warning: passing argument 1 of 'abs' makes integer from pointer without a cast [-Wint-conversion]
  abs(input,output);
      ^~~~~
/in/foo.c:3:6: note: expected 'char' but argument is of type 'char *'
 void abs(char input,char output)
      ^~~
/in/foo.c:18:12: warning: passing argument 2 of 'abs' makes integer from pointer without a cast [-Wint-conversion]
  abs(input,output);
            ^~~~~~
/in/foo.c:3:6: note: expected 'char' but argument is of type 'char *'
 void abs(char input,char output)
      ^~~