The I descriptor is used for integers in the form Iw or Iw.m. w is the field width and m is the minimum number of digits that are to be displayed. With Iw the field is padded out with leading spaces if required. With Iw.m the field is padded out with either leading spaces or leading zeros depending on the value of m. If the field width is too small for the value to be output, then the field is filled with asterisks in order to flag the error. Remember to provide space for a sign if the value might be negative.
In addition to the I descriptor, B, O, and Z are used for binary, octal and hexadecimal representations.