Looping through each element of a vector

Question

so let's say i have a vector, wich contains 4 elemens [string elements]. I need to loop through the vector first , then through each element , loop through an array of chars [vowels] and to count how many vowels does that word contain.

    for(int i = 0; i < b.size(); i++) 
    {
      for(int j = 0; j < b[i].size(); j++) 
       {
         for(int v = 0 ; v < sizeof( vowels ) / sizeof( vowels[0] ); v++)
          if(//blabla)
       }
    }

so my question is, how can i loop through each word , i mean b[i][j] is the right way to do that?

if yes, this form , will work great? :

if(b[i][j] == vowels[v]) {
//blabla
}

thanks.

Answer 1

A more advanced way to go about this, which you should take a look at if you're serious about learning C++: don't use indices and random access, use high-level STL functions. Consider:

#include <algorithm>
#include <iostream>
#include <map>
#include <numeric>
#include <set>
#include <string>
#include <vector>

bool is_vowel(char s) {
    static const char vowels[] = { 'a', 'e', 'i', 'o', 'u' };
    const char* vbegin = vowels;
    const char* vend = vowels + sizeof(vowels)/sizeof(char);
    return (std::find(vbegin, vend, s) != vend);
}

std::string::difference_type count_vowels(const std::string& s) {
    return std::count_if(s.begin(), s.end(), is_vowel);
}

template <class T> void printval(const T& obj) { std::cout << obj << std::endl; }

int main() {
    std::vector<std::string> b;
    b.push_back("test");
    b.push_back("aeolian");
    b.push_back("Mxyzptlk");

    std::vector<int> counts(b.size());
    std::transform(b.begin(), b.end(), counts.begin(), count_vowels);
    std::for_each(counts.begin(), counts.end(), printval<int>);

    int total = std::accumulate(counts.begin(), counts.end(), 0);
    printval(total);
    return 0;
}

Where the loops you've written correspond roughly to these lines:

 std::transform(b.begin(), b.end(), counts.begin(), count_vowels);
 ..
 std::count_if(s.begin(), s.end(), is_vowel);
 ..
 std::find(vbegin, vend, s)

This uses a high-level functional/generic programming idiom that C++ is not always elegant at pulling off IMO. But in this case it works fine.

See Count no of vowels in a string for a rundown of solutions to part of the problem I think you're trying to solve. You can see a variety of acceptable looping/iteration techniques on display there as well.

Answer 2

std::vector<T> defines T operator[](int). This means you can access a vector x's element i via x[i].

std::string defines char operator[](int), which returns the char at that position within the string.

So if you have an std::vector<std::string> called x, x[i][j] will return the jth character of the string in the ith position of the vector.

This is not the idiomatic C++ way to do this - the most common means would be iterators (the .begin() and .end() calls). But since vector access is constant time (as is string-character access) it's not a huge deal.