View Compilation Error

0_0_31346536_27647.cpp: In function 'int main()':
0_0_31346536_27647.cpp:25:26: error: expected ';' before ')' token
   for(int i=0;i<len_b,i++){
                          ^
0_0_31346536_27647.cpp:26:42: error: expected ')' before ';' token
    now=(a[len_a-i-1]+b[len_b-i-1]-'0'-'0';
                                          ^