the second week:
1, note the following points when cin input:
(1) The input cin, default skips spaces.
Such as:
int i; char c; float f;
cin >> i >> c >> f;
When the input 10 k 2.1, 10 does not exist after the space (c), but the presence of c, k.
Scanf input is used with a different, default is not to skip spaces:
int i; char c; float f;
scanf("%d%c%f", &i, &c, &f);
When the input 10 k 2.1, 10 will exist after the space (c), but the presence of c, k.
（2）