7.8. Our own version of find

If we are looking for a letter in a string, we may not want to start at the beginning of the string. One way to generalize the find function is to write a version that takes an additional parameter—the index where we should start looking. Here is an implementation of this function.

int find (string s, char c, int i) {
  while (i<s.length()) {
    if (s[i] == c) return i;
    i = i + 1;
  }
  return -1;
}

Instead of invoking this function on a string, like the first version of find, we have to pass the string as the first argument. The other arguments are the character we are looking for and the index where we should start.

In the active code below, we are finding the number of 'e' characters in the “Shepard” part of “German Shepard” using our function. Then we use the built-in find function to demonstrate how they work differently.

#include <iostream> #include <string> int find (std::string s, char c, int i) { int length = s.length(); while (i < length) { if (s[i] == c) { return i; } i = i + 1; } return -1; } int main() { std::string dog = "German Shepard"; int start_shepard = 7; std::cout << find(dog, 'e', start_shepard) << '\n'; std::cout << dog.find('e') << '\n'; }

Q-2: Given the definition of find provided in the previous active code, what is the correct output of the code below?

int main() {
  string quote = "The way to get started is to quit talking and begin doing.";
  cout << find(quote, 't', 11) << ", " << find(quote, 't', 42) << ", " << quote.find('t');
}

• 13, -1, 8
• Notice how the built-in find function works differently from ours.
• 13, 0, 7
• Remember that when a character isn't found, the function returns -1.
• 13, -1, 0
• Keep in mind that the find function is case sensitive, so "A" is different from "a".
• 14, -1, 9
• Remember that indexing begins at 0 for C++.

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