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Fundamentals of Software Development 1
Slide 1
Programming PatternsProgramming Patterns
• Many problems fit a Many problems fit a “pattern” that “pattern” that experienced software experienced software developers recognizedevelopers recognize– And hence can easily And hence can easily
code, from experiencecode, from experience• Previously, we saw Previously, we saw
these patterns:these patterns:– SwapSwap– Absolute valueAbsolute value– Maximum of twoMaximum of two– Select from casesSelect from cases– IncrementIncrement
• Today, we will see these Today, we will see these looping patterns:looping patterns:– Do N timesDo N times– CountCount– SumSum– Loop through a listLoop through a list– Loop followed by Loop followed by
another loopanother loop– Loop inside a loopLoop inside a loop
• Later, we will see other Later, we will see other looping patterns, looping patterns, including:including:– Max/minMax/min– Find-first in a listFind-first in a list– Do foreverDo forever– Break in the middle of a Break in the middle of a
looploop– Continue to the next Continue to the next
iteration of the loopiteration of the loop
Fundamentals of Software Development 1
Slide 2
Programming patterns Programming patterns (non-looping)(non-looping)
temp = x;x = y;y = temp;
if (y < 0) { x = -y;} else { x = y;}
if (x > y) { z = x;} else { z = y;}
swapabsolute value maximum of two
if (x >= 90) { z = ‘A’;} else if (x >= 80) { z = ‘B’;} else if (x >= 70) { z = ‘C’;} else if (x >= 60) { z = ‘D’;} else { z = ‘F’;}
x = x + 1;
Increment(for counting)
Select from cases
Keep these patterns in mind, to help you with similar problems that
you encounter
Fundamentals of Software Development 1
Slide 3
Loop pattern: “do N Loop pattern: “do N times”times”
for (int k = 8; k <= 11; k++) { System.out.print(k + ″:\t″; System.out.print(Math.pow((double) k, 0.5) + ″\t″); System.out.print(Math.pow((double) k, 0.333) + ″\t″); System.out.print(Math.pow((double) k, 0.25); System.out.println();}
• Problem 1: Display the sine of 0.01, sine of 0.02, … sine of 4.00Problem 1: Display the sine of 0.01, sine of 0.02, … sine of 4.00
for (int k = 1; k <= 400; ++k) {
System.out.println(Math.sin(k/100.0));
}
• Problem 2: Display the Problem 2: Display the 11stst, 2, 2ndnd and 3 and 3rdrd roots of roots of8 through 11, inclusive8 through 11, inclusive
8 2.8284271247461903 1.9986141859809059 3.0 2.07856091038386210 3.1622776601683795 2.15278173472437311 3.3166247903554 2.222203177024025
Note the “cast” of k to type double
Fundamentals of Software Development 1
Slide 4
Loop pattern: “do N Loop pattern: “do N times”times”
Scanner inputStream = new Scanner(System.in);int start, stop;
System.out.print(″Start at? ″);start = inputStream.nextInt();
System.out.print(″Stop at? ″);stop = inputStream.nextInt();
for (int k = start; k <= stop; k++) { Same code as in the loop in the previous example};
• Problem 3: Display the 1Problem 3: Display the 1stst, 2, 2ndnd and 3 and 3rdrd roots of roots of startstart through through stopstop, , inclusive, where inclusive, where startstart and and stopstop are determined at run time by the user are determined at run time by the user
This example also shows how to do console input
Note that start and stop are both variables here
Fundamentals of Software Development 1
Slide 5
Loop pattern: “count”Loop pattern: “count”• Problem: How many integers from -1000 to 1000, Problem: How many integers from -1000 to 1000,
inclusive, have cosines that are negative? Display inclusive, have cosines that are negative? Display the count. the count.
int count;
count = 0;for (int k = -1000; k <= 1000; ++k) { if (Math.cos((double) k) < 0 { ++ count; }}
System.out.println(count);}
Start count at 0
Increment count whenever it is time to “count”
Exercise: Sum the cosines of the integers from -20 to 2000. Display the sum.
Answer on next slide.
Fundamentals of Software Development 1
Slide 6
Loop pattern: “sum”Loop pattern: “sum”• Problem: Sum the cosines of the integers from -Problem: Sum the cosines of the integers from -
20 to 2000. Display the sum.20 to 2000. Display the sum.
double sum; sum = 0.0;for (int k = -20; k <= 2000; ++k) { sum = sum + Math.cos((double) k);} System.out.println(count);
Start sum at 0.0
Increment sum whenever it is time to “sum”, by whatever amount should be summed
sum has type double here, because the sum is of double’s
Fundamentals of Software Development 1
Slide 7
Loop pattern: “loop Loop pattern: “loop through a list”through a list”
• Problem: Write a method that returns how many Problem: Write a method that returns how many times a given character appears in a given Stringtimes a given character appears in a given String
public static int charCount(char c, String s) { int count;
count = 0; for (int k = 0; k < s.length(); ++k) { if (s.charAt(k) == c) { ++ count; } }
return count;}
A static method is one that does not use any of the fields of the class
This example includes the counting pattern
FYI: Use == only to compare primitives. To compare objects (like Strings), use their equals method, e.g. s.substring(k, k+1).equals(c + ””)
Fundamentals of Software Development 1
Slide 8
Loop followed by a Loop followed by a looploopLoop inside a loopLoop inside a loopfor (int k = 0; k < 5; ++k) {
System.out.print(k);}
for (int k = 0; k < 5; ++k) { System.out.print(k);}
for (int k = 0; k < 5; ++k) { for (int m = 0; m < 3; ++m) { System.out.print(k); }}
Same as previous box, except print m (not k)
Exercise: What output is produced by the first box to the left? By the 2nd box? The 3rd box?
0123401234
000111222333444
012012012012012
Fundamentals of Software Development 1
Slide 9
Some Some loopinglooping programming programming patternspatterns
for (int k = start; k <= stop; ++k) { do stuff}
Do N times
Keep these patterns in mind, to help you with similar
problems that you encounter
int count;
count = 0;for (some loop) { if (some condition to count) { ++ count; }}
count
Similar to count, but: sum = sum + thing-to-sum;
sum
for (int k = 0; k < s.length; ++k) { do stuff with s.charAt(k)}
Loop through a list (here, a String s)
