08-Loops.pdf

Transcript

1. ICS 212 Program Structure William McDaniel Albritton M.S.
2. Memory Allocation  Loops  while Loops  for Loops  do Loops  break Statement  continue Statement  Input/Output Redirection
4. Loops
5. Loops  Loops are used to repeat the execution of selected code
6. Counting Loop  Loops that use counters to control the number of repetitions  The counter value is increased or decreased each time the loop body is executed  The loop terminates when the counter reaches a certain value  Example: print “hello world” ten times
7. Sentinel Loop  Loops that use special values called sentinels to terminate the loop  The body of the loop is executed until the sentinel is found  For example, a program that continues calculating the interest rate and stops after the last customer  We can choose the sentinel to be the characters ‘n’ or ‘N’
8. Pre Test and Post Test Loops  When is the condition tested? false true condition statement(s) to be repeated false true condition statement(s) to be repeated
9. C Loops  C features three different kinds of loops  while loop  for loop  do loop
11. while Loop
12. while Loop  May be a sentinel or counting loop  Pre-test loop  The flowchart representation looks like this: false true condition initialization loop body update
13. while Loop  Conditions are written the same way as in if statements  The difference in the flowchart is that the loop goes back to evaluating the condition false true condition initialization loop body update
14. Infinite loop  Infinite loops happen when the condition in the while loop header is always true  It is important to verify in the body of the loop that there is a way for the condition to become false at some point  Sentinel or counting value
15. While Loop in C while (condition){ // do not forget to update }
16. Example Program  See example code at: while.c
18. for Loop
19. for Loop Structure  The most commonly used looping statement in C  Includes  An initial value  The condition  An update statement  Usually a counting loop  Pre-test loop
20. for Loop Anatomy for(initial value; condition; update){ statement1; statement2; . . . }
21. for Loop Example for(x=1; x < 11; x++){ printf(“%i\n”, x); }
22. for(x=1; x < 11; x++){ printf(“%i\n”, x); } for Loop Execution  Executes ONCE, Initialization
23. for(x=1; x < 11; x++){ printf(“%i\n”, x); } for Loop Execution  Condition Executes in each iteration
24. for(x=1; x < 11; x++){ printf(“%i\n”, x); } for Loop Execution  Update
25. Example Program  See example code at: for.c
27. do Loop
28. do Loop Structure  It is like the while loop but the condition is tested at the end  The do loop will ALWAYS EXECUTE AT LEAST ONCE  Sentinel or counting loop  Post test loop
29. do Loop Anatomy do{ statement1; statement2; . . . } while (condition);
30. do Loop Example int x = 0; do{ printf(“%i ”, x); x++; } while(x<11);
31. Example Program  See example code at: do.c
33. Break Statement
34. The Break Statement  The break statement is used to exit from a switch statement or to terminate loops
35. for(initial value; condition; update){ statement1; statement2; if(condition){ statement 3; break; } statement 4; }
36. Example Program  See example code at: break.c
38. Continue Statement
39. The Continue Statement  The continue statement is used to bypass the remainder of the current pass through a loop  The loop does not terminate because a continue statement is encountered  The loop goes back to evaluate the condition  This statement can be included within any of the loops that we know
40. for(initial value; condition; update){ statement1; statement2; if(condition){ statement 3; continue; } statement 4; }
41. int x = 1; while(x <= 10){ printf(“ %i \n”, x); x++; if(condition){ other statements; continue; } other statements; }
42. Example Program  See example code at: continue.c
43. Nested Statements  C allows structures inside other structures  Any of these inside any other  if  if/else  while  for  do  switch (case)
44. //generate multiplication table int number = 0, count = 0, product = 0; //nested for loops for(number=1; number<=MAX;number++){ for(count=1; count<=MAX; count++){ product = number * count; printf("%i * %i = %i\n", number, count, product); } printf("\n"); }
45. Example Program  See example code at: nested.c
47. Redirection in UNIX
48. I/O Redirection in UNIX  Instead of typing input for a program, you can use I/O redirection in UNIX to use a file as input or output to your program
49. I/O Redirection in UNIX  Use less-than sign (<) for input  Use greater-than sign (>) for output  Can use both as well % ./program > output.txt % ./program < input.txt % ./program < input.txt > output.txt
50. Example Program  See example code at: counting.c  Use EOF (end of file) to end the program  EOF is Ctrl-D on UNIX or Mac, Ctrl-Z on PC  Can do this with I/O redirection from a file % ./program < electricity.txt
51. Memory Management  Loops  while Loops  for Loops  do Loops  break Statement  continue Statement  Input/Output Redirection