View Compilation Error

0_0_20829577_10913.cpp: In function 'int main()':
0_0_20829577_10913.cpp:117:16: error: 'i' was not declared in this scope
     read_graph(i, j);
                ^
0_0_20829577_10913.cpp:117:19: error: 'j' was not declared in this scope
     read_graph(i, j);
                   ^