Unit 4: Decisions and Loops in Java

Unit 3 could ask whether an answer made sense and could do nothing about it, and every program so far asked its questions once and stopped. This unit finishes both. Selection arrives with parentheses and braces, conditions that are genuinely boolean, else if in two words, comparing text correctly, and the and, or and not operators. Switch is taught as the menu case. Repetition arrives as while, then the three part for header, then counting, totalling and asking again, then loops inside loops that draw a grid or a shape.

The performance task is The Pattern Engine. The student's nested loops must reproduce a printed target character for character, proven by a line by line check with a same or different mark on every line, plus a trace table covering the first three passes of the outer loop and three boundary runs at size one, a typical size and the largest size that still fits the screen. The task states in those words, before the student starts, that a program with elegant loops whose output is nearly right does not meet the standard.

Two limitations are named to students rather than hidden. A loop that computes ten results can print all ten and keep only the last one, which Unit 7 pays with arrays, and the running total is presented as the workaround it is. The pattern engine has to regenerate its output every run because there is nowhere to store it, and files are Unit 11. A teacher gets a plan and a substitute plan for each of the fifteen lessons, answer keys, tiered handouts, and grid paper style targets that can be checked by counting spaces.

The unit runs 15 instructional days.