Strange compiler error when counting letters

Question

i made a progra which sum the occurences of a letter in a string , but i get a strange error, which i can't understand.

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

int main()
{
    int sum=0;
    string sir;
    vector<int> num;
    vector<std::string> letters{"a","b","c","d","e","f","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};
    getline(cin,sir);
    for(int i = 0; i < letters.size(); i++) {
       sum = std::count(sir.begin(),sir.end(), letters[i]);

    num.push_back(sum);
    sum=0;
    }
    return 0;
}

and here ar the errors :

    c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_algo.h||In function 'typename std::iterator_traits<_InputIterator>::difference_type std::count(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator<char*, std::basic_string<char> >, _Tp = std::basic_string<char>, typename std::iterator_traits<_InputIterator>::difference_type = int]':|
E:\c\Watermelon\main.cpp:15|58|instantiated from here|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_algo.h|4591|error: no match for 'operator==' in '__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = char*, _Container = std::basic_string<char>, __gnu_cxx::__normal_iterator<_Iterator, _Container>::reference = char&]() == __value'|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_algo.h|4591|note: candidates are:|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\functional|2233|note: template<class _Res, class ... _Args> bool std::operator==(std::nullptr_t, const std::function<_Res(_ArgTypes ...)>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\functional|2227|note: template<class _Res, class ... _Args> bool std::operator==(const std::function<_Res(_ArgTypes ...)>&, std::nullptr_t)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\tuple|575|note: template<class ... _TElements, class ... _UElements> bool std::operator==(const std::tuple<_TElements ...>&, const std::tuple<_Elements ...>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|5322|note: template<class _RealType> bool std::operator==(const std::piecewise_linear_distribution<_RealType>&, const std::piecewise_linear_distribution<_RealType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|5080|note: template<class _RealType> bool std::operator==(const std::piecewise_constant_distribution<_RealType>&, const std::piecewise_constant_distribution<_RealType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|4841|note: template<class _IntType> bool std::operator==(const std::discrete_distribution<_IntType>&, const std::discrete_distribution<_IntType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|4609|note: template<class _RealType> bool std::operator==(const std::extreme_value_distribution<_RealType>&, const std::extreme_value_distribution<_RealType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|4434|note: template<class _RealType> bool std::operator==(const std::weibull_distribution<_RealType>&, const std::weibull_distribution<_RealType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|4259|note: template<class _RealType> bool std::operator==(const std::exponential_distribution<_RealType>&, const std::exponential_distribution<_RealType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|2459|note: template<class _RealType1> bool std::operator==(const std::gamma_distribution<_RealType>&, const std::gamma_distribution<_RealType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|3715|note: template<class _IntType> bool std::operator==(const std::geometric_distribution<_IntType>&, const std::geometric_distribution<_IntType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.tcc|1684|note: template<class _RealType1> bool std::operator==(const std::normal_distribution<_RealType>&, const std::normal_distribution<_RealType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|3337|note: bool std::operator==(const std::bernoulli_distribution&, const std::bernoulli_distribution&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|3337|note:   no known conversion for argument 1 from 'char' to 'const std::bernoulli_distribution&'|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|2798|note: template<class _RealType> bool std::operator==(const std::cauchy_distribution<_RealType>&, const std::cauchy_distribution<_RealType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|1906|note: template<class _IntType> bool std::operator==(const std::uniform_real_distribution<_IntType>&, const std::uniform_real_distribution<_IntType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\random.h|1725|note: template<class _IntType> bool std::operator==(const std::uniform_int_distribution<_IntType>&, const std::uniform_int_distribution<_IntType>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_vector.h|1273|note: template<class _Tp, class _Alloc> bool std::operator==(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\streambuf_iterator.h|194|note: template<class _CharT, class _Traits> bool std::operator==(const std::istreambuf_iterator<_CharT, _Traits>&, const std::istreambuf_iterator<_CharT, _Traits>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\basic_string.h|2460|note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\basic_string.h|2448|note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\basic_string.h|2434|note: template<class _CharT> typename __gnu_cxx::__enable_if<std::__is_char<_Tp>::__value, bool>::__type std::operator==(const std::basic_string<_CharT>&, const std::basic_string<_CharT>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\basic_string.h|2427|note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\allocator.h|127|note: template<class _Tp> bool std::operator==(const std::allocator<_Tp1>&, const std::allocator<_Tp1>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\allocator.h|122|note: template<class _T1, class _T2> bool std::operator==(const std::allocator<_T1>&, const std::allocator<_T2>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_iterator.h|1031|note: template<class _Iterator> bool std::operator==(const std::move_iterator<_Iterator>&, const std::move_iterator<_Iterator>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_iterator.h|1025|note: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_iterator.h|335|note: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_iterator.h|285|note: template<class _Iterator> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_pair.h|201|note: template<class _T1, class _T2> constexpr bool std::operator==(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\postypes.h|218|note: template<class _StateT> bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\ext\new_allocator.h|123|note: template<class _Tp> bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator<_Tp>&, const __gnu_cxx::new_allocator<_Tp>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_iterator.h|805|note: template<class _Iterator, class _Container> bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator<_Iterator, _Container>&, const __gnu_cxx::__normal_iterator<_Iterator, _Container>&)|
c:\mingw\bin\..\lib\gcc\mingw32\4.6.2\include\c++\bits\stl_iterator.h|799|note: template<class _IteratorL, class _IteratorR, class _Container> bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator<_IteratorL, _Container>&, const __gnu_cxx::__normal_iterator<_IteratorR, _Container>&)|
||=== Build finished: 36 errors, 0 warnings ===|

Answer 1

I guess this is a homework excersise.

You are marking it rather complicated. Try the following

1. Create an array of length 26, initialise all values to zero.
2. Get the line.
3. Take each character in turn. Make it lower case. Check if between a-z. Convert a->0, b->1 etc
4. Increment the corresponding integer in the array created in 1

You can then print out the array with the corresponding number of letters found in the line.

Answer 2

value_type of sir is char, but letters[i] is std::string. You can't compare a string with a char. Try the following instead:

vector<char> letters{'a','b','c','d','e','f','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};