压缩5个for循环，将一个数组显示为1？

Question

Is there a way to condense five for-loops into one and have them display different variables and letters for each? Currently, I have one loop with five other loops and if/else to keep it condense, but this seems redundant and defeats the very purpose of making the loop.

So I decided to post the whole source code so people can understand what I am trying to get at more. This is a program that creates 100 random grades everytime it runs and I have to sort them, then display them. I am aware I could do 5 for loops, but I want to write code that is more condensed and efficient.

The hard part is writing a loop that can display 5 arrays consistently even though the size of the array changes every run.

#include <iostream>
#include <vector>
using namespace std;

int main(){
    int grades[100];
    int sizeA=0, sizeB=0, sizeC=0, sizeD=0, sizeF=0;
    std::vector<int> gradeA, gradeB, gradeC, gradeD, gradeF;

    srand(time(NULL));

    for(int i = 0; i < 100; i++){
        grades[i] = rand() % 100 + 1;  
    }

    for(int i = 0; i < 100; i++){
        if (grades[i] < 100 || grades[i] > 0){
            if (grades[i]>=90)
                gradeA.push_back(grades[i]);
            else if (grades[i]>=70)
                gradeB.push_back(grades[i]);
            else if (grades[i]>=50)
                gradeC.push_back(grades[i]);
            else if (grades[i]>=20)
                gradeD.push_back(grades[i]);
            else if (grades[i])
                gradeF.push_back(grades[i]);
        } else {
            cout << "uhh.. ";
            return(0);
        }
    }

    sizeA = gradeA.size();
    sizeB = gradeB.size();
    sizeC = gradeC.size();
    sizeD = gradeD.size();
    sizeF = gradeF.size();


    /**toggle ? showgrades(gradeA, size) : (int?)null;**/

}   

Answer 1

How about using a function to do the looping and call it with the required information

void printGrades(const std::vector<int>& grades, char level) {
  cout << num << " " << level << " students: ";
  for(int i = 0; i < grades.size(); i++){
    cout << grades[i] << " ";
  cout << endl;
}

So when you want to print them all:

printGrades(gradeA, 'A');
printGrades(gradeB, 'B');
printGrades(gradeC, 'C');
printGrades(gradeD, 'D');
printGrades(gradeF, 'F');

Answer 2

If I were you, I would create a class Student, and then a 2D array, where every row would represent the student's category, and the number of columns of a row, the number of students.

That could be represented as a fixed-sized array of size 5, where every cell would be a std::vector of class Student .

Minimal working example:

#include <iostream>
#include <vector>

using namespace std;

class Student {
public:
    Student(int grade, char category) : grade(grade), category(category) {}
    int getGrade(void) { return grade; }
    char getCategory(void) { return category; }
private:
    int grade;     // 0, ..., 20
    char category; // A, ..., F
};

int main(void) {
    vector<class Student> std[5]; // cell 0 is for A students, ..., cel 4 is for F students
    std[0].push_back({20, 'A'}); std[0].push_back({19, 'A'});
    std[1].push_back({15, 'B'});
    std[2].push_back({17, 'C'}); std[2].push_back({17, 'C'});
    std[3].push_back({14, 'D'});
    std[4].push_back({15, 'F'});

    for (int i = 0; i < 5; ++i) {
        if(std[i].size()) {
            cout << std[i].size() << " " << std[i][0].getCategory() << " students: ";
            for (auto& student : std[i]) {
                cout << student.getGrade() << " ";
            }
            cout << endl;
        }     
    }
    return 0;
}

Output:

2 A students: 20 19 
1 B students: 15 
2 C students: 17 17 
1 D students: 14 
1 F students: 15

---

Appendix:

I understand that you want to make the code compact, but this:

for(int a = 0; a < sizeA; a++){
    cout << gradeA[a] << " ";
} aS = 1; bS = 0; cout << endl;

is not cool, since it's not readable for the reader. I suggest you to change it to:

for(int a = 0; a < sizeA; a++){
    cout << gradeA[a] << " ";
}
aS = 1;
bS = 0;
cout << endl;

since a reader expects to see no code after the closing curly bracket. That's a general statement.