Before we do more elaborate things with strings, some more string methods will be helpful. Be sure you are familiar with the earlier discussion of strings in Basic String Operations.
Play with the new string methods in csharp!
This variation of IndexOf has a second parameter:
Returns the index of the beginning of the first occurrence of the string target in this string object, starting at index start or after. Returns -1 if target is not found. Example:
csharp> string state = "Mississippi";
csharp> print("01234567890\n"+state) // to see indices
01234567890
Mississippi
csharp> state.IndexOf("is", 0); // same as state.IndexOf("is");
1
csharp> state.IndexOf("is", 2);
4
csharp> state.IndexOf("is", 5);
-1
csharp> state.IndexOf("i", 5);
7
Returns a string formed from this string object, but with leading and trailing whitespace removed. Example:
csharp> string s = "\n 123 ";
csharp> "#" + s + "#";
#
123 #
csharp> "#" + s.Trim() + "#";
#123#
Returns a string formed from this string by replacing all occurrences of the substring target by replacement. Example:
csharp> string s = "This is it!";
csharp> s.Replace(" ", "/");
"This/is/it!"
csharp> s.Replace("is", "at");
"That at it!"
csharp> "oooooh".Replace("oo", "ah");
"ahahoh"
Returns true if this string object starts with string prefix, and false otherwise. Example:
csharp> "-123".StartsWith("-");
true
csharp> "downstairs".StartsWith("down");
true
csharp> "1 - 2 - 3".StartsWith("-");
false
Returns true if this string object ends with string suffix, and false otherwise. Example:
csharp> "-123".EndsWith("-");
false
csharp> "downstairs".EndsWith("airs");
true
csharp> "downstairs".EndsWith("air");
false
Write a program TestCountRep.cs, with a Main testing method, that tests a function with the following heading:
/**Return the number of separate repetitions of target
* in s. */
static int CountRep(string s, string target)
For example here is what CountRep( "Mississippi", target) would return with various values for target:
"i": 4"is": 2"sss": 0
Assume each repetition is completely separate, so CountRep("Wheee!", "ee") returns 1. The last two e’s do not count, since the middle e is already used in the match of the first two e’s.
Save the example SafeNumberInputStub.cs as SafeNumberInput.cs.
The idea is to write safe versions of the utility functions InputInt and InputDouble (which can then be used in further places like InputIntInRange).
Be sure you are familiar with Safe Whole Number Input Exercise, and the development of its InputWhole function.
A legal whole number string consists entirely of digits. We have already written example IsDigits to identify a string for a whole number.
The improvements to InputInt and InputDouble are very similar and straightforward if you have developed the two main Boolean support functions, IsIntString and``IsDecimalString`` respectively.
The issue with integer and decimal strings is that they may include parts other than digits. An integer may start with a minus sign. A decimal number can also contain a decimal point in an appropriate place. The suggestion is to confirm that these other characters appear in legal places, remove them, and see that what is left is digits. The recently introduced string methods should help....
Develop the functions in order and test after each one: write IsIntString, revise InputInt, write IsDecimalString, and revise InputDouble.
Be sure to test carefully. Not only confirm that all appropriate strings return true: Also be sure to test that you return false" for all sorts of bad strings.
Hopefully you learned something from writing the earlier InputWhole. Probably it is not worth keeping in our utility library any longer, since we have the more general and safe InputInt, and we can restrict to many ranges with InputIntInRange.