View Compilation Error

0_0_18164567_418.c: In function 'check':
0_0_18164567_418.c:24:5: error: expected expression before '/' token
     // ac bd
     ^
0_0_18164567_418.c:27:5: error: expected expression before '/' token
     // ad bc
     ^
0_0_18164567_418.c:30:5: error: expected expression before '/' token
     // ab cd
     ^
0_0_18164567_418.c: In function 'main':
0_0_18164567_418.c:37:5: error: expected expression before '/' token
     //freopen("in.txt", "r", stdin);
     ^