View Compilation Error

0_0_2885279_30872.cpp: In function `void build_graph()':
0_0_2885279_30872.cpp:49: error: `x' undeclared (first use this function)
0_0_2885279_30872.cpp:49: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_2885279_30872.cpp: At global scope:
0_0_2885279_30872.cpp:82: error: invalid function declaration