View Compilation Error

0_0_11724056_26841.cpp:18: error: expected `,' or `;' before "const"
0_0_11724056_26841.cpp: In function `double solve()':
0_0_11724056_26841.cpp:72: error: `dx' undeclared (first use this function)
0_0_11724056_26841.cpp:72: error: (Each undeclared identifier is reported only once for each function it appears in.)