Created SC2017 (markdown)

SC2017.md

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+## Increase precision by replacing a/b*c with a*c/b.
+
+### Problematic code:
+
+    percent=$((count/total*100))
+
+### Correct code:
+
+    percent=$((count*100/total))
+
+### Rationale:
+
+If integer division is performed before multiplication, the intermediate result will be truncated causing a loss of precision. 
+
+In this case, if  `count=1` and `total=2`, then the problematic code results in `percent=0`, while the correct code gives `percent=50`.
+
+### Exceptions:
+
+If you want and expect truncation you can ignore this message. 
+
+ShellCheck doesn't warn when `b` and `c` are identical expressions, e.g. `a/10*10`, under the assumption that the intent is to rounded to the nearest 10 rather than the no-op of multiply by `1`.