Department of Computer and Information Science, School of Science, IUPUI

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Department of Computer and Information
Science,School of Science, IUPUI
A First C Program (mixing datatypes)
Dale Roberts, Lecturer Computer Science,
IUPUI E-mail droberts_at_cs.iupui.edu
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Data Type Conversion

• Rule 1
• char, short ? int
• float ? double
• Rule 2 (double ? long ? unsigned ? int)
• If either operand is double, the other is
  converted to double, and the result is double
• Otherwise, if either operand is long, the other
  is converted to long, and the result is long
• Otherwise, if either operand is unsigned, the
  other is converted to unsigned, and the result is
  unsigned
• Otherwise, the operand must be int

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Examples

• Example c char, u unsigned, i int, d
  double, ffloat,
• s short, l long,
• Expression Final Data Type Explanation
• c s / i int short?int, int/int,
  char?int, int-int
• u 3 i unsigned int(3)?unsigned,
• unsignedunsignedunsigned,
• int?unsigned, unsigned-unsignedunsigned
• u 3.0 i double unsigned?double,
  doubledouble,
• int?double, double-doubledouble
• c i int char?int
• c 1.0 double char?int (rule 1),
  int?double(rule 2)
• 3 s l long short?int, intint, int?long,
  longlong

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Data Type Conversion (cont.)

• Note
• Conversion of int to long preserves sign, so does
  short
• Var expr
• f d / round off /
• i f
• / truncates fractions part, if the number is too
  big to fit, the result is undetermined /
• i l s i and c i / may eliminate high
  order bits /

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• If a specific type is required, the following
  syntax may be used, called cast operator.
• (type) expr
• Example
• float f2.5
• x (int)f 1
• / the result is 3, Q will f value be changed?
  /
• Unsigned int to int
• there is not actual conversion between int and
  unsigned int.
• Example(Assuming 2s complement machine and int
  is 2 bytes long)
• unsigned i 65535 int j
• j i / j will be 1 /
• j -2
• unsigned i 1 j / i 65535 /