Может ли кто-нибудь помочь преобразовать C++ в C?

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#include <iostream>
#include <string>

using namespace std;

string modifiedSentence(string str, int len);
string sortedSentence(string sentence, int length);

int main(){
    string sentence = "";
    double length = 0;

    cout << "Prepared by ABC"<<endl;
    cout << "Class XYZ"<<endl;
    cout << "This program will take in a sentence from you and invert the letters in each individual words"<<endl;
    cout << "Type in a sentence with no more than 100 characters including space: "<<endl;
    getline (cin,sentence);
    length = sentence.length();
    cout << "String length is "<<length<<endl;
    cout << "The original sentence is "<<sentence<<endl;
    cout << "The modified sentence is "<<modifiedSentence(sentence, length)<<endl;
    cout << "The sorted sentence is "<<sortedSentence(sentence, length)<<endl;
    return 0;
}

string modifiedSentence(string str, int len) {
    int i, j, k;
    char tmp;

    for(i = 0, j = 0; j < len; j++){
        if(!isalpha(str[j]) || (j == len - 1)){
            if(j < len - 1){
                k = j - 1;
            } else {
                k = j;
            }

            while( i < k){
                tmp = str[i];
                str[i] = str[k];
                str[k] = tmp;
                i++;
                k--;
            }
            i = j + 1;
        }
    }
    return str;
}

string sortedSentence(string sentence, int length){
    string lower = "";
    string upper = "";
    string num = "";
    string symbols = "";
    int temp;
    for (int i = 0; i<sentence.length(); i++){
        if(islower(sentence[i])){
            lower += sentence[i];
        }
        if(isupper(sentence[i])){
            upper += sentence[i];
        }
        if(isdigit(sentence[i])){
            num += sentence[i];
        }
        if(!isalnum(sentence[i])){
            symbols += sentence[i];
        }
    }

    for (int i = 0; i<lower.length(); i++) {
        for (int j = i + 1; j < lower.length(); j++) {
            if (lower[i] > lower[j]) {
                temp = lower[i];
                lower[i] = lower[j];
                lower[j] = temp;
            }
        }
    }
    for (int i = 0; i<upper.length(); i++) {
        for (int j = i + 1; j < upper.length(); j++) {
            if (upper[i] > upper[j]) {
                temp = upper[i];
                upper[i] = upper[j];
                upper[j] = temp;
            }
        }
    }
    for (int i = 0; i<num.length(); i++) {
        for (int j = i + 1; j < num.length(); j++) {
            if (num[i] > num[j]) {
                temp = num[i];
                num[i] = num[j];
                num[j] = temp;
            }
        }
    }

    return lower+upper+num+symbols;
}

Что я уже пробовал:

Кто-нибудь может помочь преобразовать C++ в C? потому что я был новичком в программировании и мой запрос на назначение использовать C. Спасибо

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