# Difference between revisions of "FormattingDecimals"

## Formatting Decimals: PG Code Snippet

We show how to format decimals for display in PG problems. Note that these are insertions, not a complete PG file. This code will have to be incorporated into the problem file on which you are working.

PG problem file Explanation

Initialization: Standard.

\$a = random(3,7,1);
# log is natural log, and ln is also natural log
\$b = sprintf("%0.3f", log(\$a)/log(10) );

Setup: Use perl's sprintf( format, number ); command to format the decimal. The "%0.3f" portion truncates after 3 decimal places and uses zeros (not spaces) to right-justify. For answers involving money, you should set "%0.2f" for two decimal places and zero filling (for example, sprintf("%0.2f",0.5); returns 0.50). You can do a web search for more options to perl's sprintf, and also for WeBWorK's contextCurrency.pl. If you do further calculations with \$b, be aware that numerical error may be an issue since you've reduced the number of decimal places.

We used the logarithm change of base formula log10(a) = log(a) / log(10) = ln(a) / ln(10) to get a logarithm base 10.

Note: If we load MathObjects.pl, then log and ln are both defined to be the natural logarithm (base e, not base 10). If we had loaded the older PGauxiliaryFunctions.pl macro instead, then ln would be undefined and log would be defined as the natural logarithm (base e, not base 10).

BEGIN_TEXT

\( \$b = \) \{ ans_rule(20) \}

END_TEXT

Main Text: Display the formatted number.

ANS( \$b->cmp() );