需要一些帮助在我的程序中发现逻辑错误

Question

I am learning C++ through Bjarne Stroustrup's "Programming Principles and Practices Using C++" second edition. I am committed to doing all the drills and exercises because I am taking a game AI class in a month at school and I need to know C++ and I want to know as much as possible.

Anyways, if anyone has ever done the drill in the book, I am on Chapter 4's drill. I am at the very end. The final product is supposed to be a program that takes a number followed by a unit of measurement (cm, in, ft, or m) in a while loop while keeping track of the biggest value as well as the smallest value and total sum of units entered in meters. I am working entirely in meters except for the biggest and smallest values which are converted to meters to check which one is bigger but stored as they were originally entered by the user. The numbers are also inserted into a vector which isn't used until the very end to sort the values and print them in order.

Anyways, I seem to have no issue keeping track of total meters because it prints out correctly at the end but when it comes to smallest value something seems to go wrong as well as occasionally on the biggest value. Plus, some values are completely off in the vector of values. I will but the code bellow. I think the error is somewhere in my toMeters() but I have stared at it for so long that I feel like a fresh set of eyes might be helpful. Thanks!

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>

using namespace std;

constexpr double mToCm = 100.00; //1m == 100cm
constexpr double inToCm = 2.54; //1in == 2.54cm
constexpr double ftToIn = 12.00; //1ft == 12in

//this function just increases total ammount of units in meters
double adder(string unit, double total, double num)
{
    if(unit == "cm")
    {
        total += (num / mToCm);
    }
    else if(unit == "in")
    {
        double temp;
        temp = num * inToCm;
        total += (temp / mToCm);
    }
    else if(unit == "ft")
    {
        double temp;
        temp = num * ftToIn;
        temp *= inToCm;
        total += (temp / mToCm);
    }
    else
    {
        total += num;
    }
    return total;
}

double toMeters(string unit, double num)
{
    double value = num;

    if(unit == "cm")
    {
        value /= mToCm;
    }
    else if(unit == "in")
    {
        value *= inToCm;
        value /= mToCm;
    }
    else if(unit == "ft")
    {
        value *= ftToIn;
        value *= inToCm;
        value /= mToCm;
    }
    return value;
}

int main()
{

    double num, biggest, smallest; //current number, biggest and smallest value
    double total = 0; //total number in meters
    string unit, biggestUnit, smallestUnit; //current unit, unit for biggest and smallest value
    int count = 0; //count for the loop it's only real purpose is on the first and second loop runs
    vector<double>meters; //a vector of doubles called meters


    cout << "Total ammount of units will be converted to meters, largest and biggest values will be kept in original units\n";
    cout << "Start of by entering a number followed by cm, m, in, ft and continue until you want to stop; to stop, press |\n";

    while(cin >> num >> unit)
    {
        //check if user want to stop
        if(num == '|')
        {
            break;
        }

        //check for correct units, if not then break out
        if(unit != "cm" && unit != "m" && unit != "in" && unit != "ft")
        {
            cout << "Unit not recognized; only cm, m, in, ft are valid\n";
            return 1;
        }
        //this checks if there is no second unit but since cin reads no 
        //whitespace it doesn't work. I just haven't gotten around to removing it
        else if(unit == " ")
        {
            cout << "Please input a unit\n";
            return 1;
        }

        //all values in vectors are supposed to be in meters. If the unit is not 
        //in meters, we will call a push back on the value returned by converting 
        //the orignal number to meters
        if(unit != "m")
        {
            meters.push_back(toMeters(unit, num));
        }
        //else, just call a push_back
        else
        {
            meters.push_back(num);
        }

        //if the count is 0, i.e. very first run of the program, biggest and 
        //smallest is equal to original and call adder() to increment the total
        if(count == 0)
        {
            biggest = smallest = num;
            biggestUnit = smallestUnit = unit;

            total = adder(unit, total, num);
        }
        //else, if count is > 0, i.e. this is not the first run, do this part
        else
        {   
            //if the value returned after running toMeters on the current value
            //is greater than the biggest, biggest now equals current num and 
            //biggest unit is equal to current unit. Then call adder to inceare total
            if(toMeters(unit, num) > toMeters(biggestUnit, biggest))
            {
                biggest = num;
                biggestUnit = unit;

                total = adder(unit, total, num);
            }
            //same as top function but for smallers value
            else if(toMeters(unit, num) < toMeters(smallestUnit, smallest))
            {
                smallest = num;
                smallestUnit = unit;

                total = adder(unit, total, num);
            }
            //else both numbers are equal so just make a call to adder()
            else
            {
                total = adder(unit, total, num);
            }
        }
        //increase count just because. It was really only needed to be incremented once 
        ++count;
    }

    //call sort on the vector then print out the total units followed by bigges the smallest values
    //then the values in meters, is ascending sorted order.
    sort(meters.begin(), meters.end());
    cout << "Total units in meters is " << total << "\n";
    cout << "Largest unit is " << biggest << biggestUnit << "\n";
    cout << "Smallest unit is " << smallest << smallestUnit << "\n";
    cout<< "Here are all values you entered, in meters, in ascending order: \n";

    for(int i : meters)
    {
        cout << meters[i] << "m" << " ";
    }
    cout << "\n";
}

My latest inputs were 1 cm 2 in 3 m 4 ft and the output was Total units in meters is 4.28 Largest unit is 3m (correct) Smallest unit is 2in (should be 1cm) Here are all values you entered, in meters, in ascending order: 0.01m 0.01m 0.0508m 3m

Answer 1

You don't set biggestUnit or smallestUnit when you set biggest and smallest on the first input. So the comparisons don't work correctly.

Try:

    //if the count is 0, i.e. very first run of the program, biggest and 
    //smallest is equal to original and call adder() to increment the total
    if(count == 0)
    {
        biggest = smallest = num;
        biggestUnit = smallestUnit = unit;

        total = adder(unit, total, num);
    }

Also, it's not a good idea to put total = adder(unit, total, num); in every code path. Just place it once outside the if s. Otherwise, it's harder to see that it is always executed precisely once for each input.