将值分别插入地图

Question

Hello,
I am making a program in C++ in which i have used a std::map to insert two values (char, int) in which every char (a,b,c,d) is related to it's occurence in the alphabet system(1,2,3,4), so that, if I sort the alphabets, their numbers also get sorted. I know a better way is by Substracting the ACSII values and all, but this is part of a bigger code and I am interested in maps.

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Now, in my program, the user enters the characters {a, b, c} in an unsorted way and then(after entering the characters) they enter the number of their choice for every aphabet respective to what they entered before (something like custom alphabet system).
I know how to enter values in a map using

 MyMap.insert(pair <char, int> ('a', 1)); 

but in this case the user enters all the characters first and then all the numbers so I can't use the pair function. I also don't want to store the values in an array and then after receiving the int value, inserting them into the map. I want to know if there is a direct method to insert the values of the chars first and then their corresponding values(If possible, a better way than inserting the {char value, 0} and then editing the 0 to the number.).

Any help is greatly appreciated!!

Answer 1

first you could use some error indication for your map, ie. -1 to indicate that no number was given for the character. Then you could add values wihtout knowing the actual mapped value and change them later. However maps wont store values in the order you inserted them, see binary tree . Hence you would have to store the order of incoming characters sperately. But if you store the characters anyway and require a mapping for each of them there is no point in creating map entries wihtout having sufficient information about their values. I would suggest to first store all characters and insert all values while you are reading the user defined value for this character. Here is a small example. You can try it on c++ shell .

#include <iostream>
#include <map>
#include <vector>

using namespace std;

int main() {
    const size_t numberOfCharacters = 3;

    cout << "Please provide the characters you want to map" << endl;
    vector<char> characterSequence{numberOfCharacters, -1};
    for(size_t i = 0; i < numberOfCharacters; ++i) {
        cout << i << ": ";
        cin >> characterSequence[i];
    }

    map<char, int> userDefinedCharacterMapping;
    cout << endl << "Please provide the characters mapped values" << endl;
    for(size_t i = 0; i < numberOfCharacters; ++i) {
        const auto iCharacter = characterSequence[i];
        cout << iCharacter << ": ";
        cin >> userDefinedCharacterMapping[iCharacter];
    }

    cout << endl << "Your result:" << endl;
    for(const auto& iUserDefinedCharacterMapping : userDefinedCharacterMapping) {
        cout << iUserDefinedCharacterMapping.first << " -> " << iUserDefinedCharacterMapping.second << endl;
    }

    return 0;
}

Here a sample output where map iterates the characters in a different order then entered.

Please provide the characters you want to map
0: b
1: q
2: a

Please provide the characters mapped values
b: 0
q: -10
a: 13

Your result:
a -> 13
b -> 0
q -> -10