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Every integer type has an integer conversion rank that determines how conversions are performed. The ranking is based on the concept that each integer type contains at least as many bits as the types ranked below it. The following rules for determining integer conversion rank are defined in the C Standard, Section section 6.3.1.1 [ISO/IEC 9899:2011]:

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The programmer must be careful when performing operations on mixed types. This noncompliant code example shows an idiosyncrasy of integer promotions.:

int si = -1;
unsigned int ui = 1;
printf("%d\n", si < ui);

In this example, the comparison operator operates on a signed int and an unsigned int. By the conversion rules, si is converted to an unsigned int. Because −1 cannot be represented as an unsigned int value, the −1 is converted to UINT_MAX in accordance with the C Standard, Section section 6.3.1.3, paragraph 2 [ISO/IEC 9899:2011]:

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The noncompliant code example can be modified to produce the intuitive result by forcing the comparison to be performed using signed int values.:

int si = -1;
unsigned ui = 1;
printf("%d\n", si < (int)ui);

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This noncompliant code example demonstrates how performing bitwise operations on integer types smaller than int may have unexpected results.:

uint8_t port = 0x5a;
uint8_t result_8 = ( ~port ) >> 4;

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Compliant Solution

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