Main.c:2:1: error: unknown type name 'using' using namespace std; ^ Main.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std' using namespace std; ^ Main.c: In function 'main': Main.c:6:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d",&a,&b); ^