IDL Exercise 7
The purpose of this exercise is to gain an understanding of the operation and use of the control statements FOR, WHILE, IF and CASE. 

 
  1. Write a program that uses the FOR loop to compute the cumulative total over an array of values. Create a file in your account with this program and test it by plotting the cumulative sum of the numbers up to 100.

    FUNCTION CUM_TOTAL,x
    ;+
    ; y=CUM_TOTAL(x) is an array of the same size as x in which
    ; each element is the sum of itself and all lower-index elements.
    ; 
    ; EXAMPLE
    ; x=FINDGEN(10)
    ; y=CUM_TOTAL(x)
    ; PLOT,x,y
    ;
    ;-
    y=x*0B     ; Create an array of zeros the same size as x.
    N=N_ELEMENTS(x)
    y[0]=x[0]
    FOR i=1,N-1 DO y[i]=y[i-1]+x[i]
    RETURN,y
    END

  2. Use the CUM_TOTAL to find and plot the sum of the squares of all of the numbers up to 100.

  3. Write a program to simulate a gambling game. This program uses RANDOMN to generate random numbers. Use this program to generate plots of gambling results for a variety of values of D and b.

    FUNCTION Gamble,D,b
    ;+
    ; r=Gamble(D,b) returns the amount of winnings after each repetition
    ; of the gambling game. The program stops when D dollars are either
    ; won or lost. The game is assumed to have a bias b in favor of the
    ; house. A negative value of b is a bias in favor of the player. The
    ; program uses a WHILE loop and has a limit of 10,000 plays.
    ;
    ;EXAMPLE
    ; r=gamble(10,0.1)
    ; plot,r
    ;-
    s=0

    4. r=FLTARR(10001)
    n=0L

    WHILE ABS(s) LE D AND n LT 10000 DO BEGIN
        s=s+RANDOMN(seed)-b
        n=n+1
        r[n]=s
    ENDWHILE
    RETURN,r[0:n]
    END
     

  4. Write a program to determine the type of a variable. Test it with a variety of variable types that you create. An example of such a program is contained in the notes on IF.

  5. Write a program that you could use as a directory of information about people. Populate the program with data for at least six people and test it for examples of people in the directory and those not in the directory.

  6. EXERCISE FOR SUBMISSION
    Write a program for a function IMSIZE that will return the number of bits in an image of a given size. The operation of the function is described by the header information given below. You have to create the function that does this. The results should be submitted to the instructor.
    ;+
    ; s=IMSIZE(M,N,G) returns the number of bits required for an image
    ; of size M columns by N rows having G gray levels. The function returns
    ; s=-1 if G is not a positive integer.
    ;-


    7.