C++ reading sentences

string a = MwZwXxZwDwJrBxHrHxMrGrJrGwHxMrFrZrZrDrKwZxLrZrFwZxErMrXxArZw;

Assume i have this data in my string . I want to record how many M , Z , X , D , J (including those capital letters i didn't mentions ) in in string how can do it ? My friends say use vector can do it but i does not really know how to use vector is there any alternative way to do it .

I tried using for loops to do and find the M , and reset the pointer to 0 to continue find the next capital value , but not sure is there any easier way to do it .