有人可以在我的代码中找到与 C++ 中的 IF STATEMENT 相关的问题吗？

Question

#include <iostream>
using namespace std;
int max_of_four(int q, int w, int e, int r)
{
    int x;
    if( q > w &&  q > e &&  q > r)
        {int x = q;}
    else if( w > q &&  w > e && w > r)
        {int x = w;}
    else if( e > w &&  e > q &&  e > r)
        {int x = e;}
    else if( r > w &&  r > e &&  r > q)
        {int x = r;}
    else{x = 0;}   
    return x;
}
int main() {
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    cout << max_of_four(a, b, c, d);
    return 0;
}

it always outputs 0, no matter what the input is.

I suppose the I am missing something in the if statement condition, someone please help!

Answer 1

In the if's int x = q; defines a new variable x and does not modify the x you return later.

You probably just want x = q; to assign a new value to x . This also applies to the other if's.

Or you could skip the assignment alltogether:

int max_of_four(int q, int w, int e, int r)
{
    if( q > w &&  q > e &&  q > r)
        { return q; }
    else if( w > q &&  w > e && w > r)
        { return w; }
    else if( e > w &&  e > q &&  e > r)
        { return e; }
    else if( r > w &&  r > e &&  r > q)
        { return r; }

    return 0;
}

Answer 2

Actually, if you have C++11 or later, then std::max() can take an initializer list as its argument(s):

int max_of_four(int q, int w, int e, int r)
{
    return std::max({ q, w, e, r }); // Need to #include <algorithm> for std::max
}

Answer 3

Apart from redefinition of variable x, your test conditions, could be trimmed, are insufficient when values of q, w, e or r are same. Also logically the return value should be either of the four variables but it should never return a zero.

   int max_of_four(int q, int w, int e, int r)
   {
       int max = q;
       if (w > max ) max = w;
       if (e > max ) max = e;
       if (r > max ) max = r;
       return max;
   }