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    <h3>Integer types</h3> <p>It's a bad idea to use <em>most</em> <strong>integer data types</strong> to represent currencies, because of:</p> <ul> <li>a very <strong>limited</strong> representable value <strong>range</strong> in respect to common applications;</li> <li>imposing <strong>extra burden</strong> on handling <strong>fractional values</strong>.</li> </ul> <p>Specifically, the limited value range may be a serious problem with shorter integer type. Lets consider a common 32-bit signed integer (usually a <code>int</code>):</p> <ul> <li>the value range is from approx. -2.15 billion to +2.15 billion — this itself is not an option for just <em>any</em> accounting / banking / serious finance use;</li> <li>when just two last digits are used to represent the fractional part, the range shrinks to -21.5 <em>million</em> to +21.5 <em>million</em>;</li> <li>in case multiplication shall work (not speaking about mixed-precision calculations), the range is scaled down even more. </li> </ul> <p>With a 64-bit signed integer (usually a <code>long</code>) you can count up to 92 thousand trillion. When thinking about the global economy, money is being counted in trillions — hence this is neither a reasonable option.</p> <h3>Floating-point types</h3> <p>It's a bad idea to use <strong>floating-point data types</strong>, because they are <strong>imprecise</strong> in nature, which is fatal problem for the vast majority of monetary calculations.</p> <h3>Suitable data types</h3> <p>It's a very good idea to use fixed-point or decimal data types, because they usually don't have the negative properties as floating-point and integer data types:</p> <ul> <li>representable value range is broad enough;</li> <li>precision can be adjusted by rounding in respect to calculation requirements;</li> <li>no confusion thanks to natural fractional values handling;</li> <li>precise decimal number representation.</li> </ul> <p>Last but not least, the suitable data type heavily depends on the language and its capabilities.</p> <h3>Other problems</h3> <p>Also, in many calculation scenarios it is necessary to use different precision for intermediate calculations and for the resulting values. While results usually have to be represented with the precision defined for the particular currency by the respective law, intermediate calculations may involve higher-precision intermediate results. Examples are percentage calculations in loan payments, insurance costs, etc., or currency conversions where exchange rates are frequently given in higher precision.</p> <p>Multi-currency softwares also need to deal with the fact that different currencies have different lawful precisions. Rounding may be imposed by accounting standards.</p>
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    1. POWhy don't applications typically use int to internally represent currency values?
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    1. USOndrej Tucny
    1. USOndrej Tucny
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    1. COOndrej, good point about intermediate calculations. With an int representing currency, you would effectively forcing a round to the nearest penny after each and every step of a multi-step calculation, which may not be requirements call for. Can you clarify / elaborate on your other point regarding "very limited representable range"?
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      1. USJon Schneider
    2. COEdited my answer to explain more.
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      1. USOndrej Tucny
    3. COIf a program is going to be used to calculate world economic data accurate to the penny, a 64-bit integer may not suffice, but how many programs are going to be used for that? In most financial calculations, even 32-bit integers would be sufficient for storing most values if one could accommodate intermediate calculations spilling out to 64 bits before being scaled back down.
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      1. USsupercat
 

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