/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:6:24: error: expected expression before '=' token
  for(int i=0;input[i]!=='0';i++)
                        ^
/in/foo.c:7:3: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   if(input[i]='a'||input[i]='e'||input[i]='i'||input[i]='o'||input[i]='u')
   ^~