View Compilation Error

0_0_35652787_32360.cpp: In function 'int main()':
0_0_35652787_32360.cpp:20:28: error: 'pop' was not declared in this scope
                 pop(x, y, b);
                            ^
0_0_35652787_32360.cpp:22:28: error: 'pop' was not declared in this scope
                 pop(y, x, b);
                            ^