Hi again, took the advice given to me and last night in I played around with the code trying out different things until I came to the code below. I did try putting in do while loop before the switch but kept getting a error, so could some tell me were to put it? I tidied up the code a bit too. I think there no more mistakes now.I would have fixed the program the first time but I lost the disk with the code and as I said I just found it.

Code:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/*
Author :A.Mac Hugh
Date: 31-8-2003
Version:1.1 beta*/
void engery ();         /* function   */
void lenght ();
void time_1 ();      /*  prototypes*/
void momentum ();
void mass ();
void Kenetic_Eng ();
void st();


#define c 3E8

int main()
{
int menu (); /* function prototype*/

     printf("\n\tWelcome to Machsofts Einstine calculator.\n"
      "\tThis program will \n\t "
      "calculate all of the equatios for Einstines Theroy of Special General Relativity.");
	 printf("\n\tThis is copyright Machsoft INC 2002");
	 printf("\n\tVersion 1.1 Beta\n\n\n");/* intoduction*/

	 

	 menu (); /*fuction beging run*/

return menu();

}

int menu (){
int nums;
/* ask user for therir option*/
   printf("\n\n\n");
   printf("\n\n\nSlect from 1-0 and  hit enter after  choice\n\n");
   printf("\t\tTo calculate Engery  press \t\t\t(1)\n");
   printf("\t\tTo calculate Lenght contraction press \t\t(2)\n");
   printf("\t\tTo calculate Time dialation press \t\t(3)\n");
   printf("\t\tTo calculate Relativistic Momentum \t\t(4)\n");
   printf("\t\tTo calculate Relarive Mass  press \t\t(5)\n");
   printf("\t\tTo calculate Kenetic Engery \t\t\t(6)\n");
   printf("\n\t\t\tTo exit  press (0) then enter\n");

scanf("%d",& nums);/*get option*/

 /*Switich statment for chosesing option*/

switch (nums){


       case 0:
       exit(0);
       break;

       case 1 :
       engery();
       printf("\n\n)");
       break;

       case 2:
       lenght();
       printf("\n\n)");
       break;

       case 3:
       time_1();
       printf("\n\n)");
       break;

       case 4:
       momentum();
       printf("\n\n)");
       break;

       case 5:
       mass();
       printf("\n\n)");
       break;

       case 6:
       Kenetic_Eng();
       printf("\n\n)");
       break;

       case 1701:
       st();
       printf("\n\n)");
       break;

       default:/*invalid option*/
       printf("\aInvaiid Option \n\nEnter choice again \n\n");
       printf("\n\n\n");
       break;

             }
 
 }





/* Fuction name :engery
 
Fuction varibles( All floats) : e engery
                                m mass
				   

Purpose: Ask user to enter in the mass.Works out the engery .

Prints out engery in joules*/

void engery (){     

float e;
float m;

    printf("This works out Mister Einstein most famous equation E=MC squared\n\nE=Engery\n\nM=Mass\n\n C = The speed of light\n\n");
    printf(" Please enter in the values for the mass (m)\nand press enter\n\n" );/*ask user enter in values*/
    scanf("%f",&m);/* get values*/

    e=c*c*m;

    printf("\nThe Engery is %e joules \n\t\n",e);/* prints out engery*/



}

 /* Fuction name :lenght
 
Fuction varibles( All doubles) : l_0 orignal lenght 
				                l_1 lenght 
				                v velocity 

Purpose: Ask user to enter in the orignal lenght and velocity.Works out lenght.
Prints out lenght*/
void lenght (){     
float l_0 ;
float l_1;
float v;


	printf("This works Lenght contraction equation\n\n ");
	printf(" Please enter in the values for \nthe orgnal lenght and the velocity \nPress enter after each value\n \n");/*ask user enter in values*/
	scanf("%f%f",&l_0,&v);/* get values*/

    l_1=l_0*sqrt(1-(v*v)/(c*c));

    printf("\nThe lenght is %e meters\n\t\n",l_1);/* prints out lenght */

}

/* Fuction name :time
 
Fuction varibles( All floats) : t_0 time at rest
                                 t time
								 v velocity
                                
				   
				    

Purpose: Ask user to enter in the time at rest.Works out works time.
Prints out time*/
void time_1 (){
float t ;
float t_1;
float v;



	printf("This works Time dialation equation\n\n ");
	printf(" Please enter in the values for\n the time at rest and the velocity.\nPressenter after each vaule\n\n");/*ask user enter in values*/
	scanf("%f%f",&t_1,&v);/* get values*/

    t=t_1/sqrt(1-(v*v)/(c*c));

    printf("\n\n\n\n\n\n\nThe time is %e seconds\n\t\n",t);/* prints out time */

}


/* Fuction name :momentum
 
Fuction varibles( All floats) :  m_0 orignal mass
                                 p  momentum
								 v velocity
                                
				   
				    

Purpose: Ask user to enter in the ogrignal mass and velocity.Works out works momentum.
Prints out momentum*/
void momentum (){
float p ;
float m_0;
float v;

	printf("This works  equation Relativistic Momentum\n\n");
	printf(" Please enter in the values \nfor the orignal mass and the velocity \nPress enter after each value\n\n");/*ask user enter in values*/
	scanf("%f%f",&m_0,&v);/* get values*/

	p=(m_0)*(v)/sqrt(1-(v*v)/(c*c));

    printf("\nThe momentum is %e\n\t\n",p);/* prints out momentum*/

}

/* Fuction name :Kenetic_Eng
 
Fuction varibles( All floats) :  m_0 ogrignal mas
                                 v velocity
								 ke kentic_Eng
                                
				   
				    

Purpose: Ask user to entert in the ogrignal mass and velocity.Works out works kentic engery.
Prints out Kentic engery*/
void Kenetic_Eng (){
float ke ;
float m_0;
float v;

	printf("This works   Kenetic Engery equation");
	printf(" Please enter in the values for \nthe orignal mass and the velocity \n Press enter after each value\n");/*ask user enter in values*/
	scanf("%f%f",&m_0,&v);/* get values*/

	ke=(m_0)*(c)*sqrt(1-(v*v)/(c*c));

    printf("\nThe Kenetic Engery is %e\n\t\n",ke);/* prints out KE*/

}

/* Fuction name :mass
 
Fuction varibles( floats) :      m_0 ogrignal mas
                                 v velocity
								 m kentic_Eng
                                
				   
				    

Purpose: Ask user to entert in the ogrignal mass and velocity.Works out works mass.
Prints out mass*/
void mass (){
float m;
float m_0;
float v;

      printf("This works Relarive Mass equation\n\n ");
      printf(" Please enter in the values \nfor the orignal mass   and the velocity \nPress enter after each value\n\n");/*ask user enter in values*/
      scanf("%f%f",&m_0,&v);/* get values*/

      m=(m_0)/sqrt(1-(v*v)/(c*c));

      printf("\nThe momentum is %e \n\n\n",m);/* prints out mass*/

 

}
  /*Ester Egg fuction*/
void st(){

    printf( "\n\nUSS ENTERPRISE NCC-1701-E\n\n\n LAUNCHED IN 2372\n\n\nCO CAPTIAN JEAN -LUC PICARD\n\n\n XO  CRMD.WILLIAM T RIKER\n\n\n 2ND XO LT.CRMD DATA\n\n\n");


                                /*prints out ester egg.What do you think???????*/

    }