View Compilation Error

0_0_37432622_4805.cpp: In function 'int main()':
0_0_37432622_4805.cpp:25:35: error: 's' was not declared in this scope
                 else if(i > 1 && (s[i-2] == '+' || s[i-2] == '*') && s[i-1] == '0' && s[i] == '?')
                                   ^