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Noncompliant Code Example

One way to check whether a number is even or odd is to examine the least significant bit. This will give inconsistent results. Specifically, this example will give unexpected behavior on all ones' complement implementations.

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int value;

if (scanf("%d", &value) == 1) {
  if (value & 0x1 == 1) {
    /* do something if value is odd */
  }
}

Compliant Solution

The same thing can be achieved compliantly using the modulo operator.

int value;

if (scanf("%d", &value) == 1) {
  if (value % 2 == 1) {
    /* do something if value is odd */
  }
}

Risk Assessment

Incorrect assumptions about integer representation can lead to execution of unintended code branches and other unexpected behavior.

References

\[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.2.6.2