View Compilation Error

0_0_29459047_30922.cpp: In function 'int main()':
0_0_29459047_30922.cpp:6:16: error: 'scanf' was not declared in this scope
  scanf("%d", &n);
                ^
0_0_29459047_30922.cpp:7:10: error: 'getchar' was not declared in this scope
  getchar();
          ^
0_0_29459047_30922.cpp:15:10: error: 'gets' was not declared in this scope
   gets(ch);
          ^
0_0_29459047_30922.cpp:16:18: error: 'strlen' was not declared in this scope
   len = strlen(ch);
                  ^
0_0_29459047_30922.cpp:42:59: error: 'printf' was not declared in this scope
     printf("a:%d\ne:%d\ni:%d\no:%d\nu:%d\n", a, e, i, o, u);
                                                           ^
0_0_29459047_30922.cpp:46:56: error: 'printf' was not declared in this scope
     printf("a:%d\ne:%d\ni:%d\no:%d\nu:%d\n\n",a,e,i,o,u);
                                                        ^