为什么“i”是未声明的标识符？(c++)

Question

`代码错误的图像

我可以将“i”用于课程，但不能用于成绩。我查看了其他示例，它们也做同样的事情，允许“i”出现在成绩部分。

#include <iostream>

using namespace std;

int main() {
  float course1;
  float grade1;
  float totalhour =0;
  float points;
  float totalpoints =0;
  for(int i = 1; i <=4; ++i)
  cout << "Course " << i << "hours" ;
  cin >> course1;

  cout << "Grade for course " << i << endl;
  cin >> grade1;
}

错误：使用未声明的标识符 'i' cout << "Grade for course" << i << endl; ^

Answer 1

因为i是在for循环中声明的，所以只能在循环中使用。

如果你想重复多件事，你应该用{}.

#include <iostream>

using namespace std;

int main() {
  float course1;
  float grade1;
  float totalhour =0;
  float points;
  float totalpoints =0;
  for(int i = 1; i <=4; ++i) {
    cout << "Course " << i << "hours" ;
    cin >> course1;

    cout << "Grade for course " << i << endl;
    cin >> grade1;
  }
}

如果你只想i在循环之后使用，你应该在循环之前声明。

#include <iostream>

using namespace std;

int main() {
  float course1;
  float grade1;
  float totalhour =0;
  float points;
  float totalpoints =0;
  int i;
  for(i = 1; i <=4; ++i)
  cout << "Course " << i << "hours" ;
  cin >> course1;

  cout << "Grade for course " << i << endl; // i will be 5 here
  cin >> grade1;
}