Compilare: user.cpp: In function ‘void concat(char*, char*, int, int)’: user.cpp:17:15: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] a[strlen(a)]=NULL; ^ user.cpp: In function ‘int main()’: user.cpp:29:21: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] a[strlen(buffer)-1]=NULL; ^ user.cpp:33:21: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] b[strlen(buffer)-1]=NULL; ^ user.cpp:26:32: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(buffer,sizeof(buffer),f); ^ user.cpp:30:32: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(buffer,sizeof(buffer),f); ^ user.cpp:35:19: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f,"%d",&m); ^ user.cpp:39:23: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f,"%d",&v[i]); ^