Question 1
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#include <iostream>

using namespace std;


float findAverage(int mark[]){


}
int findMax(int mark[]){


}

int findMin(int mark[]){


}

float findMeanDev(int mark[]){


}
int main(){
    int mark[10] = {80,75,91,82,87,95,65,49,55,77};
    int option;
    
    cout << "Input option:" << endl;
    cout << "\t1. Average" << endl;
    cout << "\t2. Highest mark" << endl;
    cout << "\t3. Lowest mark" << endl;
    cout << "\t4. Mean deviation" << endl;
    cout << ">";
    cin >> option;
    switch(option){
        case 1: cout << "Average = " << findAverage(mark) << endl; break;
        case 2: cout << "Average = " << findMax(mark) << endl; break;
        case 3: cout << "Average = " << findMin(mark) << endl; break;
        case 4: cout << "Mean Deviation = " << findMeanDev(mark) << endl; break;
        default: cout << "Error" << endl;
        
    }
    return 0;
}
===============================================================

Question 2
-----------------------------------------------------------
#include <iostream>

using namespace std;

void findstring(string sentence){


}

void extractString(string sentence){


}

void countVowel(string sentence){


}
int main(){
    string sentence;
    int option;
    cout << "Input a sentence: ";
    getline(cin,sentence);
    cout << "Input option:" << endl;
    cout << "\t1. Find a string" << endl;
    cout << "\t2. Extract string" << endl;
    cout << "\t3. count vowel" << endl;
    cout << ">";
    cin >> option;
    switch(option){
        case 1: 
            findstring(sentence); 
            break;
        case 2: 
            extractString(sentence);
            break;
        case 3: 
            countVowel(sentence);
            break;

        default: 
            cout << "Error" << endl;
        
    }
    return 0;
}