C语言请教，请问这段代码哪里出错了呢?为什么没法实现这个题目的要求呢？

#include<stdio.h>
int main()
{
int second_function(int parameter);
float profit,total_commission,else_,part_1,part_2,part_3,part_4,part_5,part_6;
int grade,parameter;
scanf("%f",&profit);
if (profit<=100000) {grade=1;parameter=1;}
 else if (profit<=200000)  {grade=2;parameter=2;}
  else if (profit<=400000) {grade=3;parameter=3;}
   else if (profit<=600000)  {grade=4;parameter=4;}
    else if (profit<=1000000)  {grade=5;parameter=5;}
     else grade=6;parameter=6;
switch(grade)
{
 case 6:part_1=(1.0/100)*(profit-1000000);else_=second_function(parameter);total_commission=part_1+else_;break;
 case 5:part_2=(1.5/100)*(profit-600000);else_=second_function(parameter);total_commission=part_2+else_;break;
 case 4:part_3=(3.0/100)*(profit-400000);else_=second_function(parameter);total_commission=part_3+else_;break;
 case 3:part_4=(5.0/100)*(profit-200000);else_=second_function(parameter);total_commission=part_4+else_;break;
 case 2:part_5=(7.5/100)*(profit-100000);else_=second_function(parameter);total_commission=part_5+else_;break;
 case 1:part_6=(10.0/100)*profit;total_commission=part_6; 
}
printf("The total commission is %f",total_commission);
return 0;
}
int second_function(int parameter)
{
float part_2,part_3,part_4,part_5,part_6;
part_2=part_3=part_4=part_5=part_6=0.0;
switch(parameter)
 {case 6:part_2=(1.5/100)*400000;
  case 5:part_3=(3.0/100)*200000;
  case 4:part_4=(5.0/100)*200000;
  case 3:part_5=(7.5/100)*100000;
  case 2:part_6==(10.0/100)*100000;
  return (part_2+part_3+part_4+part_5+part_6);
  }
}

 我要修改我的回答了，题目看着有点绕，好久没写代码了

 是不是因为int second_function(int parameter)没有返回值呀，函数类型为int，则需要有返回值，switch里面的return是返回switch的，并且最后一个case好像有两个等号，你试试看行不行

int second_function(int parameter)
{
float part_2,part_3,part_4,part_5,part_6;
part_2=part_3=part_4=part_5=part_6=0.0;
switch(parameter)
 {case 6:part_2=(1.5/100)*400000;
  case 5:part_3=(3.0/100)*200000;
  case 4:part_4=(5.0/100)*200000;
  case 3:part_5=(7.5/100)*100000;
  case 2:part_6==(10.0/100)*100000;
  }
  return (part_2+part_3+part_4+part_5+part_6);
}