View Compilation Error

0_0_37451644_22386.cpp: In function 'int solve()':
0_0_37451644_22386.cpp:21:15: error: 'x' was not declared in this scope
  for(len = 0; x > 0; x /= 10) {
               ^
0_0_37451644_22386.cpp: In function 'int main()':
0_0_37451644_22386.cpp:31:25: error: too many arguments to function 'int solve()'
   printf("%d\n", solve(m) - solve(n - 1));
                         ^
0_0_37451644_22386.cpp:19:5: note: declared here
 int solve() {
     ^
0_0_37451644_22386.cpp:31:40: error: too many arguments to function 'int solve()'
   printf("%d\n", solve(m) - solve(n - 1));
                                        ^
0_0_37451644_22386.cpp:19:5: note: declared here
 int solve() {
     ^