Write a function to calculate the exchange rate of pounds to dollars 

Answer

      Td = 2xTp
 
The parameter passed over is the number of pounds and returned the value in dollars

    float  convert (float x )
    { 
      float  y ;
/*A function which converts pounds   measure X to a dollars measure*/
    /*The parameter x is real and a real value y  is  returned*/
       y = 2.0  * x;
       return (y);
    }
The program which calls the function would be
    include
    include
    include
    include
    include
    void  main()
    {
    char prompt;
     float  a, b;
    printf("please enter in your value in pounds  \n\r");
     scanf("%f",&a);
     b= convert(a);
     printf("The value in dollars  is %5.3f \n\r",b);
     b= convert(3.0);
     printf("The value in dollars of 3 pounds   is %5.3f \n\r",b);   
    printf("Press any key to exit \n\r");
    scanf("\n%c",&prompt);
    }

 Here the program requests the value of a in pounds, then executes function 'Convert'. This causes the program to go to the function statement, pass the variable a, to it and the output is passed back to the program. The output is then assigned to variable b and printed out. It is possible to pass a value over instead of a variable. The only amendment we have to make is to add the prototype to the program i.e.

    float convert (float);
 
This describes the type of variables passed to and from the function. Therefore the complete program and function is shown below 
 
    include
    include
    include
    include
    include
    float  convert (float);
    void main()
    {
    char prompt;
     float  a, b;
    printf("please enter in your in pounds \n\r");
     scanf("%f",&a);
     b= convert(a);
     printf("The value in dollars is %5.3f \n\r",b);
     b= convert(3.0);
     printf("The value in dollars  of 3 pounds is %5.3f \n\r",b);   
                        printf("Press any key to exit \n\r");
    scanf("\n%c",&prompt);
    }
 
    float  convert (float x )
    { 
      float  y ;
/*A function which converts pounds   measure X to a dollars measure*/
    /*The parameter x is real and a real value y  is  returned*/
     
        y = 2.0  * x;
       return (y);
    }