使用C ++的编程原理和实践第4章钻取，第7步

Question

I'm working my way through Programming Principles and Practice Using C++ and I'm stuck on step 7 of the chapter 4 drill. I've found similar questions here, but something isn't working right with converting the units/values and seeing which is larger/smaller. The program runs fine, but for some reason certain conversions aren't coming back correct such as if I enter 2 m, and then 2 ft. 2 ft comes back as the larger value.

I know the code probably looks a bit ugly, I'll put the conversion in a function if I can get this to work. Thanks in advance.

int main() {
double doubNum = 0;
double smallestNum = ' ';
double largestNum = 0;
string unitOfDistance = " ";
double testNum = 0;

cout << "Enter a distance with a unit of measure (ft, in, cm, m): ";

while (cin >> doubNum >> unitOfDistance) { //while tests to see if the input is a double and unit is legal

    //check the unitOfDistance and convert all values to cm and hold in testNum for comparison
    if (unitOfDistance == "in") { //in to cm
        testNum = doubNum * 2.54;
    }
    else if (unitOfDistance == "ft") { //ft to cm
        testNum = (doubNum * 12) * 2.54;
    }
    else if (unitOfDistance == "cm") { //cm
        testNum = doubNum;
    }
    else if (unitOfDistance == "m") { //m to cm
        testNum = doubNum * 100;
    }
    else {
        cout << "I don't know that unit.\n";
        return 0;
    }

    //check to see if testNum (the converted version of doubNum) is the smallest/largest/same value entered so far
    if (testNum < smallestNum) {
        smallestNum = doubNum;
        cout << smallestNum << " " << unitOfDistance << " is the smallest distance entered so far.\n";

    }
    else if (testNum > largestNum) {
        largestNum = doubNum;
        cout << largestNum << " " << unitOfDistance << " is the largest distance entered so far.\n";

    }
    else {
        cout << smallestNum << " " << unitOfDistance << " is the smallest distance entered so far.\n";
        cout << largestNum << " " << unitOfDistance << " is the largest distance entered so far.\n";
    }

    cout << "Enter another distance with unit: \n";
}}

Answer 1

Try this

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

int main() {
    double num, result, smallest, largest;
    smallest = numeric_limits<double>::max();
    largest = numeric_limits<double>::min();
    string unit;
    cout << "Enter a distance with a unit of measure (ft, in, cm, m): ";
    while (cin >> num >> unit) {
        if (unit == "in")       // in to cm
            result = num * 2.54;
        else if (unit == "ft")  // ft to cm
            result = (num * 12) * 2.54;
        else if (unit == "cm")  // cm
            result = num;
        else if (unit == "m")   // m to cm
            result = num * 100;
        else {
            cout << "I don't know that unit.\n";
            break;
        }
        smallest = min(smallest, result);
        largest = max(largest, result);
        cout << smallest << " cm is the smallest distance entered so far.\n";
        cout << largest << " cm is the largest distance entered so far.\n";
    }
    return 0;
}

Input

2 m
3 ft
6 in

Output

Enter a distance with a unit of measure (ft, in, cm, m):
200 cm is the smallest distance entered so far.
200 cm is the largest distance entered so far.
91.44 cm is the smallest distance entered so far.
200 cm is the largest distance entered so far.
15.24 cm is the smallest distance entered so far.
200 cm is the largest distance entered so far.

Answer 2

There are few problems with your code :
1. double smallestNum = ' ' should be replaced with double smallestNum = DBL_MAX (or a really large value).
2.Just as you have used largestNum and smallestNum to keep track of largest and smallest values, you also need to use unitOfLargestDistance and unitOfSmallestDistance to keep track of their corresponding units.
3.

if (testNum < smallestNum) {
    smallestNum = doubNum;
    cout << smallestNum << " " << unitOfDistance << " is the smallest distance entered so far.\n";
}

Here you need to update smallestNum with testNum not doubNum . So it should be like:

if (testNum < smallestNum) {
    smallestNum = testNum;
    cout << doubNum << " " << unitOfDistance << " is the smallest distance entered so far.\n";
}

Similarly for the other 2 conditions.