I have problem with this simple code. The program counts the letters in the string / vector.

I have two methods, one for vector and one for string. In main(), on the first line, I want to use the method for vector in first parameter, and on the second line I want to use the method for string. But both commands are using the string method.

#include <iostream>
#include <vector>
using namespace std;

int How_many_vector=0;
int How_many_string=0;

int count_chars(vector<char>& word, char character){
    for(int i = 0; i <=word.size();i  ){
        if(word[i]==character){
            How_many_vector  ;
        }
    }

    return How_many_vector;
}

int count_chars(string wordstring,char character){
    for(int i = 0;i<=wordstring.length();i  ){
        if (wordstring[i]==character){
            How_many_string  ;
        }
    }
    return How_many_string;
}

int main(){
    cout<< count_chars({'t','a','b','t','z'},'t')<<endl;
    cout<<count_chars("balcer",'b');
}

CodePudding user response：

Both std::vector and std::string can be constructed from a brace list. So you have to be more explicit about which function you actually want to call when passing it a brace list.

You can't bind a vector& reference to a brace list. And you can't bind it to a temporary vector, either. So the 1st line can't call the vector version of the function.

However, a string object can be constructed from a brace list, and the string version of the function takes a string by value, not by reference. So, the 1st line can (and does) call the string version of the function, by creating a temporary string from the brace list, and then passing that temporary to the function.

If you want to call the vector version instead, you will have to call it with a pre-existing vector object for the vector& reference to bind to:

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int count_chars(vector<char>& word, char character){
    int How_many = 0;
    for(size_t i = 0; i < word.size();   i){
        if (word[i] == character){
              How_many;
        }
    }
    return How_many;
}

int count_chars(string wordstring, char character){
    int How_many = 0;
    for(size_t i = 0; i < wordstring.length();   i){
        if (wordstring[i] == character){
              How_many;
        }
    }
    return How_many;
}

int main(){
    vector<char> vec{'t','a','b','t','z'};
    cout << count_chars(vec, 't') << endl;
    cout << count_chars("balcer", 'b');
}

If you don't want to declare a separate variable, then change the vector& reference to const vector& instead (which you should do anyway, since the function is just reading values, not modifying them), and then you can construct a temporary vector object directly in the parameter for it to bind to (as a const reference can bind to a temporary):

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int count_chars(const vector<char>& word, char character){
    int How_many = 0;
    for(size_t i = 0; i < word.size();   i){
        if (word[i] == character){
              How_many;
        }
    }
    return How_many;
}

int count_chars(const string &wordstring, char character){
    int How_many = 0;
    for(int i = 0; i < wordstring.length();   i){
        if (wordstring[i] == character){
              How_many;
        }
    }
    return How_many;
}

int main(){
    cout << count_chars(vector<char>{'t','a','b','t','z'}, 't') << endl;
    cout << count_chars("balcer", 'b');
}

And just FYI, both of your functions are redundant, as the standard library has a std::count() algorithm for counting the number of occurrences of a given value in a range of values, such as vectors and strings.

CodePudding user response：

"simple as possible" is quite simple, you do that by using library functions. By the way, code on this site is licensed cc-by-sa, so you need to cite me when you hand this in:

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>

using std::count;

int main() {
    std::vector<char> v{'t', 'a', 'b', 't', 'z'};
    std::string s("balcer");

    std::cout << count(v.begin(), v.end(), 't') << "\n"
              << count(s.begin(), s.end(), 'b') << "\n";
}

CodePudding user response：

Here's code for counting letters in a string:

unsigned int letter_quantity(const std::string& s)
{
    unsigned int quantity = 0;
    const unsigned int length = s.length();
    for (unsigned int i = 0; i < length;   i)
    {
        if (std::isalpha(s[i]))   quantity;
    }
    return quantity;
}

This is simple. Increments a count for every letter in a std::string. The code can be adapted to using std::vector<char> as well.

You can make it more complex by writing your own letter detector:

for (unsigned int i = 0; i < length;   i)
{
    static const std::string letters[] =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        "abcdefghijklmnopqrstuvwxyz";
    std::string::size_t position = letters.find(s[i]);
    if (position != std::string::npos)   quantity;
}