View Compilation Error

0_0_20387650_19976.cpp: In function 'int main()':
0_0_20387650_19976.cpp:54:51: error: 'len' was not declared in this scope
             for(int i=2;s3[i]<='9'&&s3[i]>='0'&&i<len;++i) val=val*10+(s3[i]-'0');
                                                   ^