Question

我是C编程的新手，我最近碰到了从3个数字中找到第2大数字的问题。我尝试使用if ... else，但总是给出最小的数字作为输出。我在这段代码中犯的逻辑错误是什么？

#include<stdio.h>

int main() {
    int a;
    int b;
    int c;
    a=10;
    b=30;
    c=7;
    if(a>b) {
        if(a>c) {
            if(b>c)
                printf("2nd largest is %d",c);
            else
                printf("2nd largest is %d",b);
        }
    } else

    {
        if(b>c) {
            if(c>a)
                printf("2nd largest is %d",a);
            else
                printf("2nd largest is %d",c);
        } else
            printf("2nd largest is %d",b);
    }
}

Answer 1

if(a>b) {
    if(a>c) { //a is the greatest!
        if(b>c) // the *greater* of the two remaining is the second greatest
            printf("2nd largest is %d",c); // if b > c, output b!
        else
            printf("2nd largest is %d",b); // if c > b, output c! 
    } // I think this got missed:  What if c > a and a > b?
} else

{
    if(b>c) { //b is the greatest!
        if(c>a) //As above, the *greater* of the two remaining is what you are looking for
            printf("2nd largest is %d",a); // c is greater, so output it
        else
            printf("2nd largest is %d",c); // a is greater
    } else // c > b and b > a, this is correct.
        printf("2nd largest is %d",b);
}

Answer 2

逻辑很好，但需要交换变量的打印，如下所示

1）

        if(b>c)
            printf("2nd largest is %d",b);
        else
            printf("2nd largest is %d",c);

2）

       if(c>a)
            printf("2nd largest is %d",c);
        else
            printf("2nd largest is %d",a);

Answer 3

if(a>=b && a>=c) {   
    if(b>=c) printf("2nd largest is %d",b);
    else printf("2nd largest is %d",c);
} else if(b>=a && b>=c) {
    if(a>c=) printf("2nd largest is %d",a);
    else printf("2nd largest is %d",c);
} else if(c>=a && c>=b) {
    if(a>=b) printf("2nd largest is %d",a);
    else printf("2nd largest is %d",b);
}

或

 static int middleVal(int a, int b, int c) {
    if(a >= b && a >= c) return b > c? b : c;
    return middleVal(b,c,a);
    }

Answer 4

有很多方法可以执行这些操作，但是如果您只使用了二进制最小和最大功能：

printf("2nd largest is %d", min(min(max(a,b),max(b,c)),max(a,c)));

如果您需要更通用的选择（不仅是第二大元素，而是第k个最大元素），请使用像quickselect这样的选择算法：http://en.wikipedia.org/wiki/Quickselect#Algorithm

Answer 5

我建议你使用qsort和数组来实现这个有一个例子：

#include <stdio.h>
#include <stdlib.h>

// This is a custom function for qsort where we define the sort rules
int cmpfunc (const void * a, const void * b)
{
    return ( *(int*)b - *(int*)a );
}
int main() {
int n;

// Set the number of element
int values[]           = {10, 30, 7};

// Dynamically get the number of element 
int nbOfValue;
nbOfValue = sizeof(values) / sizeof(int);

// Set the number of element to display
int nbOfValueToDisplay = 2;


/*
    Will reorganize you array value 
*/
qsort(values, nbOfValue, sizeof(int), cmpfunc);


for (n = 0 ; n < nbOfValueToDisplay; n++ ) {
  printf("%d ", values[n]);
}

}

使用if_else从3个数字中获得第2大

5 个答案: