Next Loops

For Counter = Start To End Step Increment statements Next Counter 

Both Step Increment in the For statement, and Counter following the Next are optional. If Increment is omitted, it is set equal to 1. Increment can be negative. 

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In this method the looping yam runs transversely to the length of the fabric. Loops are formed on a row of needles and the next loops are caught in the hooks of the needles and then drawn through the first loops. Weft knitting machines normally give a circular product and can be used to form the... 

To solve the full problem of finding an approximate ground state to Hamiltonian (13), one is faced to a self-consistent loop which can be proceeded in two steps. First one can get the occupations nia)o from a HWF, and a set of bare levels. Then one obtains a set of configuration parameters, the probabilities of double occupation, di by minimizing (18) with respect to these probabilities. Afterwards the on-site levels are renormalized according to (21) and the next loop starts again for the new effective Hamiltonian He// till convergence is achieved. 

The second alternative is to direct specific samples to the NMR that are of particular interest. The sample can then be trapped in the cell and data acquired from an adequate number of pulses to provide the required resolution. Subsequently, the sample can be expelled from the cell using solvent supplied directly from the chromatography pump. The third alternative is to direct the eluent from the column to a sample loop where it can be stored until the spectrometer is available to take data. If necessary, a number of solutes can be stored in different loops and they can be examined when convenient. When the data has been acquired from one sample, the solute stored in the next loop can then be displaced into the NMR cell. Samples that have been examined can either be displaced to waste or collected for further examination. A photograph of the Varian flow control device for the LC/NMR system is shown in figure 41. 

The For Each...Next loop structure is similar to the For...Next loop structure, except that it executes the statements within the loop for each object within a group of objects. Figure 14-12 illustrates the syntax of the statement. 

An important point the For..Each...Next loop returns an object variable in each pass through the loop. You can access or use all of the properties or methods that apply to Element. For example, in a loop such as... 

Often you use a loop structure to search through an array or collection of objects, looking for a certain value or property. Once you find a match, you don t need to cycle through the rest of the loops. You can exit from the loop using the Exit For (from a For...Next loop or For Each...Next loop) or Exit Do (from a Do While... loop). The Exit statement will normally be located within an If statement. For example. 

The simple macro in Figure 16-1 formats the text in a single cell. We d like our macro to be able to format text in a single cell or in a range of cells. To do this, we simply need to add an outer For..Each...Next loop. We ll add the lines of code... 

To specify the range of cells to use as data labels, we ll use the InputBox method. We ll define the range as an object variable, so that we can use a For...Each...Next loop. For a code example, see "You Can Define Your Own Objects" in Chapter 14. To convert SeriesCollection(l) into the general case, remember that a specific item in a collection can be referred to by its index number or by its name. We ll use the code... 

Duplicate variable names can cause all sorts of problems. You might use a variable called A to hold a value at the beginning of the program, and then inadvertently use the same variable name later on. If the program returns to the beginning, the value has changed. FOR-NEXT loops sometimes lead to duplication. When you re using a variable like A, make sure you don t use it as an index in a FOR-NEXT loop. And remember, only the first two characters of a variable count the computer thinks ALT is the same variable name as ALIEN. 

To avoid doubled variables, it helps to pick certain letters to be used only in loops and as "temporary" variables. For example, decide ahead of time that you will always use J, K, and L in FOR-NEXT loops. 

When BASIC begins a FOR-NEXT loop, it writes a note about where in memory the loop begins, pushes it on the stack, and forgets about it until it comes across a NEXT statement. NEXT tells the computer that somewhere earlier in the program a FOR started a loop. It then pulls the information it needs off the stack and jumps back. 

Don t worry about adding any NEXTs, the computer will never get that far. Run the program and you ll get an OUT OF MEMORY error after only ten loops have begun. A FOR-NEXT loop uses up a lot of space on the stack—for a pointer to beginning of the loop, step size, highest value, and variable names. 

When stack problems pop up, they re often caused by a GOTO in the middle of a subroutine. It can leave some garbage on the stack. The same goes for jumping out of a FOR-NEXT loop. And too many parentheses can give you either a FORMULA TOO COMPLEX error or contribute to an OUT OF MEMORY message. As the garbage on the stack builds up, it eventually reaches the limit. 

Check free memory. If there seems to be a lot left, you may have a full stack, caused by too many unresolved FOR-NEXT loops or GOSUBs. 

Perhaps you ve narrowed it down to a certain FOR-NEXT loop. An important variable, K8, is somehow being changed. So you add a line PRINT K8 STOP, and every time the program reaches that line, it prints the value of K8 and stops. 

If your computer locks up, consider the possibility that your computer is not locked up. A FOR-NEXT loop that counts to a million takes a lot of time. So does POKEing a few thousand numbers into memory. And it s possible to write an inefficient sorting routine that takes hour, even days, to complete. In cases like these, you might want to demonstrate that there s no lockup by printing to the screen or changing border color once in a while. 

The description request flag in line 400 determines whether this section of the program is executed or skipped over. Remember that 0 indicates the latter. If it is 0, then, this entire routine is bypassed. If it is executed, describing the room consists simply of printing the appropriate element of the room descripion array. That s line 410. Then in line 430, a FOR-NEXT loop executes, which goes through each item in the item location array. For each item that s located in the current room (F = 0), it prints the corresponding element of the item description array (done in line 450 and 460). This way the player will see what each room contains. 

Before we use it, we will first explain the working of this function, line by line. The first line defines the function by its name, Smallstep, and specifies what input data the function requires. The last line specifies the end of the function. In between, the value of ais recomputed n times, using a For... next loop in lines 2 through 4, and the result is specified in line 5. These instructions are written in Visual BASIC, the language that Excel uses for its functions and macros. (Visual BASIC is a modern form of compiled BASIC, with additions to make it suitable for spreadsheet use. Section 10.12 will review some features ofVisual BASIC.)... 

Note that the third line of the function is equivalent to (9.2-18) except that Af has been replaced by At/n, which is then repeated n times in the For. .. next loop. And if you wonder where the labels wand w-1 on whave gone, the equal sign in BASIC actually means an assignment, i.e., the computer first evaluates the value of a (i-a k delt/n), then assigns that value to the variable a on the left-hand side of the equal sign. 

This example illustrates how easy it is to use a For Each. .. Next loop to address ah cells in a given, highlighted block, even without ever specifying it as an array. The name cell specifies the individual cells in the highlighted block, and the loop addresses each of them in turn. (Any other name instead of cell would have worked just as well. You can see that cell is not recognized by the VBA compiler because it is not capitalized. (But Cells in... 

Below the assignment Array = Selection.Value we encounter two nested For Next loops. In each loop a calculation is repeated a specified number of times. In this example, each numerical value in the array is in turn raised to its cube power (or to any other power we might have specified instead of 3). Incidentally, note that the indentation used facilitates our reading of the macro, by showing what lines are involved in the two different loops. 

On the other hand, the macro Power disp enses with much of this, and simply condenses steps (b) through (e) into a simple, single For Each... Next loop. 

B2+ 1= 8 + 1 =9, hence we find the result 93 = 729 instead. In B4 the macro then computes 7303 = 3.87E + 08, and from there the size of the results quickly escalates to exceed the numerical capacity of the spreadsheet (approximately 9.9 X 10307) in B8, which is why we see the overflow sign. Therefore one should use For Each... Next loops only on cells containing values that are independent of all other data in the selected block. 

The cause of the problem lies in the numbers 3 and 113 used to raise the individual terms of the array to their cube power, and to take their cube root. When we raised the individual cells in the block (or the individual elements in Array) to their cube power, we reduced the results to single precision. To demonstrate this and, at the same time, fix the problem, add a dimension statement to both macros, reading Dim p As Double , and add a line specifying the value of p (e.g., either p = 3 or p =1/3 ). Finally, in the For Each... Next (or in the nested For... Next loop) refer to p rather than to 3 (or 1/3). The macros now should read like the example shown below, where we have also added a title and some comment lines and, as before, boldfaced the most recent changes. 

There are two types of control loops. When you knowhow many times a particular procedure should be repeated, use a For...Next loop when you do not know this in advance, use a Do loop instead. 

When a For... Next loop contains only a single, short statement, it may be written on one line, with its three parts separated by colons, as in... 

For...Next loops may be nested. In that case it is good practice to use separate counters, as in... 

The For Each...Next loop is similar to a For... Next statement except that it will automatically apply the statements to each element of the specified group. The syntax is... 

The syntax of the Do...Until loop is similar except that the term While is replaced by Until . In the above example, the Do Until statement would read Do Until c > N to yield the same result. As with For... Next loops, Do loops can be nested. 

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