5.2.4  Extracting portions of a string

The left and right commands find the left and right parts of a string. (See Section 8.2.3, Section 6.5.1, Section 6.6.2, Section 6.3.6, Section 9.3.4, Section 9.3.5, Section 28.2.8 and Section 28.2.9 for other uses of left and right.)

• left takes two arguments:
  • str, a string.
  • n, a non-negative integer.
• left(str,n) returns the first n characters of the string str.
• right takes two arguments:
  • str, a string.
  • n, a non-negative integer.
• right(str,n) returns the last n characters of the string str.

The head command finds the first character of a string.

• head takes str, a string.
• head(str) returns the first character of the string str.

The mid command finds a selected part from the middle of a string.

• mid takes three arguments:
  • str, a string.
  • p, an integer for the starting index of the result.
  • q, an integer q for the length of the string.
• mid(str,p,q) returns the part of the string str starting with the character at index p with length q. (Remember that the first index is 0 in Xcas mode.)

The tail command removes the first character of a string.

• tail takes str, a string.
• tail(str) returns the string str without its first character.

Examples