C ++ if / else if语句不起作用

Question

I'm fairly new to C++ and I have to make a C++ program that sorts 3 numbers (smallest-greatest) using pass by reference. Everything works fine up until my if statement in my function. I have tried to do a lot of debugging and it seems like whenever I use "<" the statement doesn't execute. If I do (n1 > n2) the statement executes no matter what. If anyone can help that would be great. Here is my code:

#include <cstdlib>
#include <iostream>
#include <stdio.h>

using namespace std;

int sortNum(double &n1, double &n2, double &n3);

int main(int argc, char *argv[]) {
    double num1, num2, num3;

    printf("Welcome to Taylor's Sorting Program \n");
    printf("Enter 3 numbers and the program will sort them \n");
    printf("Number 1: \n");
    scanf("%d", &num1);
    printf("Number 2: \n");
    scanf("%d", &num2);
    printf("Number 3: \n");
    scanf("%d", &num3);

    sortNum(num1, num2, num3);

    printf("Sorted Values \n");
    printf("Number 1: %d ", num1);
    printf("\t Number 2: %d ", num2);
    printf("\t Number 3: %d \n", num3);

    system("PAUSE");
    return EXIT_SUCCESS;
}

int sortNum(double &num1, double &num2, double &num3) {
    double n1, n2, n3;
    n1 = num1;
    n2 = num2;
    n3 = num3;


    if (n1 < n2 && n1 > n3) {
        num1 = n2;
        num2 = n1;
        num3 = n3;
    } else if (n2 < n1 && n2 > n3) {
        num1 = n3;
        num2 = n2;
        num3 = n1;
    } else if (n3 < n2 && n3 > n1) {
        num1 = n2;
        num2 = n3;
        num3 = n1;
    }
    return 0;
}

Answer 1

You are using the wrong format specifier for scanf() . Instead of %d (signifying a pointer to an integer), use %lf (Pointer to a double ). Alternately, change double to int in your code.

Note that your printf() statements suffer from a similar problem, and should be using either %f , %g or %e .

Answer 2

There are 6 possible orders (permutations) of three different numbers.

Your code appears to check for only 3 of those, namely, in order,

n3 < n1 < n2

and

n3 < n2 < n1

and

n1 < n3 < n2

In the 3 other cases you just return 0 and that's it.

From my systematic listing above, can you guess what the three other cases have in common, how they're similar?

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By the way, not asked for, but you'll save yourself from tons of trouble by using C++ cin and cout instead of low level C functions scanf and printf .