Casts

• Often, it is useful to convert between int and float variables. For example, it is natural to want the result of dividing two ints to be a float. The C language allows you to do this via casts.

• To cast an expression to type int, prefix it with the string (int). To cast an expression to type float, prefix it with (float). Casting has higher priority than binary operators like + but the same priority as unary operators like - or ++, so (float) -35 / 47.3 casts -35 to a float, then performs the division.

• Casting an int to a float is straight forward and does what you expect. Casting a float to an int is problematic in that
  • It may cause overflow (floats can be much bigger than ints) and
  • What to do with the fractional part?
  In C, int casts can cause overflow errors and for positive floats, the fractional part is truncated down. Negative floats may be truncated up or down, depending on your compiler and computer.

• Casts are explicit type conversions. The C compiler also sometimes performs implicit type conversions in at least two cases:
  • When assigning a floating point expression to an int variable or assigning an integer expression to a float, the C compiler will cast the expression to the same type as the variable being assigned to.
  • When one operand of a binary operator is an int expression and the other is a float expression (like in 3 + 7.2), the int expression is cast to a float.