关于函数返回字符串的问题

Question

我班级的程序需要返回平均分数，具有姓氏和名字的高分以及低分。我发现查找高分和低分名称的函数时出错，但我不确定是什么问题。

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

float highestVal(float highScore, float score);
float lowestVal(float lowScore, float score);

string highFirstFun(float highScore, float score, string firstNameHigh);
string highLastFun(float highScore, float score, string lastNameHigh);
string lowFirstFun(float lowScore, float score, string firstNameLow);
string lowLastFun(float lowScore, float score, string lastNameLow);



int main() {

    ifstream inFile;
    string fileName = "", firstName = "", lastName = ""; 
    float score, average;
    float highScore = 0;
    float lowScore = 100;
    float studentNum = 0;
    float sum = 0; 
    int i;
    string highFirst = "", highLast = "";
    string lowFirst = "" , lowLast = "";
    cout << "Please enter the input file name: "; 
    cin >> fileName;
    inFile.open(fileName);

    while (!inFile.is_open()) {
        cout << "Sorry, the file did not open. \nTry again, or type \"cancel\" to quit: ";
        cin >> fileName; 
        if (fileName == "cancel") {
            cout << "Cancelling..." << endl; 
            break; 
        }
        else {
            inFile.open(fileName); 
        }
    }

    if (inFile.is_open()) {
        cout << "The scores are as follows: \n"; 
        while (!inFile.eof()) {
            inFile >> firstName >> lastName >> score; 
            cout << firstName << " " << lastName << " scored " << score << endl;
            sum += score;  
            studentNum++;
            highScore = highestVal(highScore, score);
            lowScore = lowestVal(lowScore, score);
            highFirst = highFirstFun(highScore, score, firstName);
            highLast = highLastFun(highScore, score, lastName);
            lowFirst = lowFirstFun(highScore, score, firstName);
            lowLast = lowLastFun(highScore, score, lastName);
        }

        average = (sum / studentNum);
        cout << "There are " << studentNum << " students with an average grade of " << average << endl;
        cout << "The high score was: " << highScore << " from " << highFirst << " " << highLast << endl;
        cout << "The low score was: " << lowScore << " from " << lowFirst << " " << lowLast << endl;
        inFile.close();
    }
    return 0;
}


float highestVal(float highScore, float score)
{
    if (score > highScore) {
        highScore = score; 
    }
    return (highScore);
}

float lowestVal(float lowScore, float score)
{
    if (score < lowScore) {
        lowScore = score;
    }
    return (lowScore);
}

string highFirstFun(float highScore, float score, string firstNameHigh)
{
    if (score > highScore) {

        return (firstNameHigh);
    }
}

string highLastFun(float highScore, float score, string lastNameHigh)
{
    if (score > highScore) {

        return (lastNameHigh);
    }
}

string lowFirstFun(float lowScore, float score, string firstNameLow)
{
    if (score < lowScore) {

        return (firstNameLow);
    }
}

string lowLastFun(float lowScore, float score, string lastNameLow)
{
    if (score < lowScore) {

        return (lastNameLow);
    }
}

这里是从中提取的名为“ Scores.txt”的文本文件：

John   Smith   99.0
Sarah Johnson  85.0
Jim Robinson  70.0
Mary Anderson  100.0
Michael Jackson 92.0

任何帮助将不胜感激！

Answer 1

具有返回类型的函数必须始终返回该类型。函数

string highFirstFun(float highScore, float score, string firstNameHigh);

例如，在调用string时必须始终返回。问题是您的功能的定义

string highFirstFun(float highScore, float score, string firstNameHigh)
{
    if (score > highScore) {

        return (firstNameHigh);
    }
}

highFirstFun()仅在[且仅当string高于score时才返回highScore。好吧，如果分数不高于highScore会怎样？这对于该函数将是一个问题，因为如果发生这种情况，它不会做任何事情，因此编译器会抱怨它。这适用于您的所有功能。为了使它们起作用，您必须找到一种在所有情况下都使它们返回字符串的方法。