练习（求中间大小的数）：
int main()
{
    int number1,number2,number3;
    int middle;
    scanf("%d",&number1);
    scanf("%d",&number2);
    scanf("%d",&number3);

    if(number1>=number2)
    {
        if(number3>=number1)
        {
            middle=number1;
        }
        else
        {
            if(number3>=number2)
            {
                middle=number3;
            }
            else
            {
                middle=number2;
            }
        }
    }
    else
    {
        if(number3>=number2)
        {
            middle=number2;
        }
        else
        {
            if(number3>=number1)
            {
                middle=number3;
            }
            else
            {
                middle=number1;
            }
        }
    }

    printf("%d",middle);

    return 0;
}

简化：
int main()
{
    int number1,number2,number3;
    int middle;
    scanf("%d",&number1);
    scanf("%d",&number2);
    scanf("%d",&number3);

    middle=(number1>=number2)?(number3>=number1)?number1:(number3>=number2)?number3:number2:(number3>=number2)?number2:(number3>=number1)?number3:number1;

    printf("%d",middle);

    return 0;
}

版本3：
#include <stdio.h>
#include <stdlib.h>

int main()
{
    float a,b,c;
    printf("请输入数字a:\\n");
    scanf("%f",&a);
    printf("请输入数字b:\\n");
    scanf("%f",&b);
    printf("请输入数字c:\\n");
    scanf("%f",&c);
    if((c<=a&&a<=b)||(b<=a&&a<=c))
        printf("%f",a);
    if((b<c&&c<=a)||(a<c&&c<=b))
    {
        printf("%f",c);
    }
    if((c<b&&b<=a)||(a<b&&b<=c))
    {
        printf("%f",b);
    }
    return 0;
}