balls.cpp: In function 'void backt(int)': balls.cpp:21: warning: comparison between signed and unsigned integer expressions balls.cpp:27: warning: comparison between signed and unsigned integer expressions balls.cpp:40: warning: comparison between signed and unsigned integer expressions balls.cpp:51: warning: comparison between signed and unsigned integer expressions balls.cpp: In function 'int main()': balls.cpp:83: warning: unused variable 'c1' balls.cpp:83: warning: unused variable 'c2' balls.cpp:83: warning: unused variable 'k' balls.cpp:84: warning: unused variable 'ch' balls.cpp:81: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result balls.cpp:82: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result balls.cpp:85: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result balls.cpp:86: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result /tmp/cc0jdr6W.o: In function `main': balls.cpp:(.text+0x2f6): warning: the `gets' function is dangerous and should not be used.