How do I remove errors from this program?

<pre>



<pre>#include<iostream.h>
#include<conio.h>
 float Celsius(float,float ,float , float ,int);
float Kelvin(float C,float K,float F,float ans,int y);                                     //prototypes
float Fahrenheit(float C,float K,float F,float ans,int y);
int main()
{

int x;
float answer;
cout<<"\t\t\tWElCOME TO TEMPERATURE CALCULATOR";
getch();
cout<<"\n\nSelect your first operator =>";
cout<<"\n1.Kelvin";
cout<<"\n2.Celsius";
cout<<"\n3.Fahrenheit\n\n";
cin>>x;
switch(x)
{
  case 1:float Kelvin(float C,float K,float F,float ans,int y) ;
			break;
  case 2:float Celsius(float C,float K,float F, float ans,int y)   ;
			break;
  case 3:float Fahrenheit(float C,float K,float F,float ans,int y)    ;
			break;
  }
 return 0 ;
  }                                                                                         //end of main
//------------------------------------------------------------------------------------------------------------------------------------------
float Kelvin(float C,float K,float F, float ans,int y)
{
cout<<"\nSelect your second operator =>";
cout<<"\n1.Celsius";
cout<<"\n2.Fahrenheit";
cin>>y;
switch(y)
 {case 1:cout<<"Enter Kelvin";
			cin>>K;
			C=K-273.15;
			ans=C;
			break;
  case 2:cout<<"Enter Kelvin" ;
			cin>>K;
			F=K*9/5-459.67;
			ans=F;
			break;
  }
  cout<<"your answer is "<<ans;
  return (0);
}


float Celsius(float C,float K,float F, float ans,int y)
{
cout<<"Select your second operator =>";
cout<<"\n1.Kelvin";
cout<<"\n2.Fahrenheit";
cin>>y;
switch(y)
 {case 1:cout<<"Enter Celsius";
			cin>>C;
			K=C+273.15;
			ans=K;
			break;
  case 2:cout<<"Enter Celsius" ;
			cin>>C;
			F=C*9/5+32;
			ans=F;
			break;
  }
  return ans;
}



float Fahrenheit(float C,float K,float F,float ans,int y)
{
cout<<"Select your second operator =>";
cout<<"\n1.Kelvin";
cout<<"\n2.Celsius";
cin>>y;
switch(y)
 {case 1:cout<<"Enter Fahrenheit";
			cin>>F;
			K=(F+459.67)*5/9;
			ans=K;
			break;
  case 2:cout<<"Enter Fahrenheit";
			cin>>F;
			C=(F-32)*5/9;
			ans=C;
			break;
  }
return ans;
}

the error is in 21st 23rd and 25th line inside the switch
in the function calls
i am compiling using turboc++ 4.5
i will copypaste the errorsbelow:
error FUNC.CPP 21:Expression syntax in function main()
error FUNC.CPP 23:Expression syntax in function main()
error FUNC.CPP 25:Expression syntax in function main()
i am trying to make a temperature converter using functions and some switches