loop

loop

In programming, a repetition within a program. Whenever a process must be repeated, a loop is set up to handle it. A program has a main loop and a series of minor loops, which are nested within the main loop. Learning how to set up loops is what programming technique is all about.

The following example prints an invoice. The main loop reads the order record and prints the invoice until there are no more orders to read. After printing date and name and addresses, the program prints a variable number of line items. The code that prints the line items is contained in a loop and repeated as many times as required.

Loops are accomplished by various programming structures that have a beginning, body and end. The beginning generally tests the condition that keeps the loop going. The body comprises the repeating statements, and the end is a GOTO that points back to the beginning. In assembly language, the programmer writes the GOTO, as in the following example that counts to 10.

          MOVE     "0" TO COUNTER
   LOOP   ADD      "1" TO COUNTER
          COMPARE  COUNTER TO "10"
          GOTO     LOOP IF UNEQUAL
          STOP

In high-level languages, the GOTO is generated by the interpreter or compiler; for example, the same routine as above using a WHILE loop.

       COUNTER = 0
       DO WHILE COUNTER <> 10
          COUNTER = COUNTER + 1
       ENDDO
       STOP

For a more detailed look at a loop, look at the end of the C definition. The main event loop of the DOS version of this database is presented.

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loop

1. Electronics a closed electric or magnetic circuit through which a signal can circulate

2. a flight manoeuvre in which an aircraft flies one complete circle in the vertical plane

3. Chiefly Brit a railway branch line which leaves the main line and rejoins it after a short distance

4. Maths Physics a closed curve on a graph

5. another name for antinode

6. Anatomy

a. the most common basic pattern of the human fingerprint, formed by several sharply rising U-shaped ridges

b. a bend in a tubular structure, such as the U-shaped curve in a kidney tubule (Henle's loop or loop of Henle)

7. Computing a series of instructions in a program, performed repeatedly until some specified condition is satisfied

8. Skating a jump in which the skater takes off from a back outside edge, makes one, two, or three turns in the air, and lands on the same back outside edge

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(programming)

loop - A sequence of instructions that the processor repeats, either until some condition is met, or indefinitely. In an structured language (e.g. C, Pascal, BASIC, or Fortran), a loop is usually achieved with for loop, while loop or repeat loop constructs. In other languages these constructs may be synthesised with a jump (assembly language) or a GOTO (early Fortran or BASIC).