Why Are `short` Integers Promoted to `int` Before Arithmetic Operations in C and C ?

Why Must a Short Be Converted to an Int Before Arithmetic Operations in C and C ?

In C and C , short integer types must be converted to int before performing arithmetic operations. This feature was introduced in C to provide better code performance and accuracy.

According to the rationale for the C standard, calculations performed in a "wider" type (int) can result in faster code and more accurate results. This is because int has a larger range of values than short, reducing the chances of overflow.

The usual arithmetic conversions applied to operands of arithmetic expressions dictate that short operands are first promoted to int through the integer promotions. This step ensures that calculations are performed using the wider int type, maintaining the integrity of the arithmetic operations.

Although short operands could be used for these operations, doing so can lead to incorrect results or unexpected behavior, as demonstrated in the example below:

short s = 1, t = 2 ;
auto  x = s + t ;

In this example, x will have the type int instead of short because the usual arithmetic conversions are applied. This conversion ensures that the addition operation is performed with integer values, preventing potential errors or inconsistencies.

Ultimately, the decision to convert short operands to int before arithmetic operations strikes a balance between efficiency, accuracy, and predictability. By promoting short operands to int, C and C ensure that arithmetic operations are performed correctly and without loss of data or precision.

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