Compilare: main.cpp: In function 'int main()': main.cpp:19:10: warning: converting to non-pointer type 'char' from NULL [-Wconversion-null] s[n]=NULL; ^~~~ main.cpp:154:21: warning: this 'else' clause does not guard... [-Wmisleading-indentation] else ^~~~ main.cpp:156:25: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'else' op.pop(); ^~ main.cpp:172:21: warning: this 'else' clause does not guard... [-Wmisleading-indentation] else ^~~~ main.cpp:174:25: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'else' op.pop(); ^~ main.cpp:15:33: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("bool.in","r",stdin); ^ main.cpp:16:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("bool.out","w",stdout); ^ main.cpp:17:26: warning: ignoring return value of 'char* fgets(char*, int, FILE*)', declared with attribute warn_unused_result [-Wunused-result] fgets(s+1,1005,stdin); ^ main.cpp:25:21: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n",&k); ^ main.cpp:26:26: warning: ignoring return value of 'char* fgets(char*, int, FILE*)', declared with attribute warn_unused_result [-Wunused-result] fgets(r+1,1005,stdin); ^