View Compilation Error

1_798_2164_21535.cpp: In function 'int main()':
1_798_2164_21535.cpp:3:28: error: 'scanf' was not declared in this scope
    while(scanf("%d%d",&n,&a)!=EOF){
                            ^
1_798_2164_21535.cpp:3:31: error: 'EOF' was not declared in this scope
    while(scanf("%d%d",&n,&a)!=EOF){
                               ^
1_798_2164_21535.cpp:4:28: error: 'printf' was not declared in this scope
     printf("%d\n",a+(n-a)/2);
                            ^