View Compilation Error

0_0_19050600_11258.cpp: In function 'int main()':
0_0_19050600_11258.cpp:25:16: error: 'gr' was not declared in this scope
    while( fabs(gr-gl) >= 1e-10 ){
                ^
0_0_19050600_11258.cpp:25:19: error: 'gl' was not declared in this scope
    while( fabs(gr-gl) >= 1e-10 ){
                   ^