#include<stdio.h>
void main()
{
    float a,b,c,d,a1,b1,c1,d1,t;
    char J,L,M1,M2,T;
    printf("输入a,b,c,d的值:");
    scanf("%f,%f,%f,%f",&a,&b,&c,&d);
    a1=a;
    b1=b;
    c1=c;
    d1=d;
    printf("机架为j,连架杆为m,连杆为l\n");
    printf("依次输入a,b,c,d所代表的结构:");
    scanf("%c,%c,%c,%c",&J,&L,&M1,&M2);
    if(a+b+c>d&&a+b+d>c&&a+c+d>b&&b+c+d>a)
    {
           if   (a>b)   
          {   
                  t=a;
                  a=b;
                  b=t;   
          }   
        if   (a>c)   
          {   
                  t=a;
                  a=c;
                  c=t;   
          }   
        if   (a>d)   
          {   
                  t=a;
                  a=d;
                  d=t;   
          }   
        if   (b>c)   
          {   
                  t=b;
                  b=c;
                  c=t;   
          }   
        if   (b>d)   
          {   
                  t=b;
                  b=d;
                  d=t;   
          }   
        if   (c>d)   
          {   
                  t=c;
                  c=d;
                  d=t;   
          }
        if(a+d>c+b)
            printf("此机构为双摇杆机构");
        else
            if(a1==a)
                T=J;
            if(b1==a)
                T=L;
            if(c1==a)
                T=M1;
            if(d1==a)
                T=M2;
            switch(T)
            {
                case 'm': printf("此机构为曲柄摇杆机构");break;
                case 'j': printf("此机构为双曲柄机构");break;
                case 'l': printf("双摇杆机构");break;
                default : printf("error\n");
            }

    }
    else
        printf("显示错误");
    getchar();

}
目的是输入四个数字，指定它们各自的部位一个是j，一个是l，两个是m，先判断是否组成四边形，否则输出显示错误，是则继续判断最大边和最小边之和是否小于等于其余两边和，否则输出双摇杆机构，是则继续判断，若最小边是j则为双曲柄机构，最小边是m曲柄摇杆机构，最小边l双摇杆机构~~