Strings Are Like Arrays, but Different

Some of the things you learned about arrays should remind you of things you learned about strings. Here's some similarities and differences you should keep track of.

Reminders... (array indexes and string indexes are similar)

You should be familiar with the .length(), .size(), .find(), and .substr() string functions from an earlier lab. Now that you know more about arrays, you should recognize that the index numbering for strings and arrays is similar - they both start at 0 and end at size-1. #include <iostream> #include <string> using namespace std; int main() { string testing = "one two three!"; string first = "one"; //"one" is the first word so "one" is found at position 0 int p = testing.find(first); cout << p << endl; //This method will extract the first match, if it is found if (p != string::npos) { string s; s = testing.substr(p, first.length()); cout << s << endl; } //This next method will give the same results as the last method, //but only if we don't change first to another word. //Code like this is inflexible and should be avoided. string s; s = testing.substr(0, 3); cout << s << endl; //Print the last character in the string cout << s.substr(s.size()-1,1) << endl; return 0; }

Another Array-like Feature of Strings

Strings can use the same element access notation as arrays. But, unlike arrays, they know their own length. It's found with .size() or .length() remember? So it's even easier to work with them!

Using [] with a string gives you access to the character at that position. Remember to treat the element like a character!

Here's a few tricks you should take a moment to understand: #include <iostream> #include <string> using namespace std; int main() { string testing = "one twain three"; cout << "Original:\t" << testing << endl; //Build a copy of the string with dots between each letter cout << "Extra dots:\t"; string copy; for (int i = 0; i < testing.length(); i++) { copy += testing[i]; copy += ".."; } cout << copy << endl; //Print the string backward cout << "Backward:\t"; for (int i = testing.length()-1; 0 <= i; i--) { cout << testing[i]; } cout << endl; //Find a word and replace it with stars! cout << "Censored:\t"; string word = "twain"; int p = testing.find(word); if (p != string::npos) { for (int i = p; i < (p + word.length()) ; i++) { //testing[i] = "*"; // this doesn't work!!! testing[i] = '*'; // the elements of strings are characters. } } cout << testing << endl; return 0; }

The trick used for the "Extra dots:" example is another feature strings have that arrays don't. It's still possible to append one array to another, but it takes extra work, and an array with extra space.

Passing Strings to Functions

Unlike arrays, strings are passed by value. You need to use & to pass them by reference. Also unlike arrays, you do not need to pass their size. Strings know their own size. #include <iostream> #include <string> using namespace std; void moreBs(string &); int main() { string testing = "\tBetty Botter had some butter,\n\t\"But,\" she said, \"this butter's bitter.\""; cout << "Before: " << endl << testing << endl << endl; moreBs(testing); cout << "After: " << endl << testing << endl << endl; return 0; } void moreBs(string &str) { for (int i = 0; i < str.size(); i++) { char c = tolower(str[i]); if (c == 'b' || c == 't') { str[i] = 'B'; } } }