Retrieving the first char of a string and comparing it alphabetically in C++

Question

I'm a novice programmer learning C++ through a tutorial and I want to know how I can take a string, take its first letter, compare it to the first letters of 2 other strings and then sort them alphabetically. I don't want code written for me. I want to understand how to do this because other solutions were difficult to understand.

I know that strings are just arrays of char so there should be a method to get the first index.

UPDATE

So this is my attempt:

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

void valueOutput(string firstName, string secondName, string thirdName){
    cout << "\n";
    cout << firstName << endl;
    cout << secondName << endl;
    cout << thirdName << endl;
}

int main(){
    string name1, name2, name3;

    cout<<"Enter 3 names: "<<endl;

    cin>>name1;
    cin>>name2;
    cin>>name3;

    if(
       (name1[0] < name2[0] && name2[0] < name3[0]) 
    || (name1[0] < name3[0] && name3[0] < name2[0])
    || (name2[0] < name1[0] && name1[0] < name3[0])
    || (name2[0] < name3[0] && name3[0] < name1[0])
    || (name3[0] < name1[0] && name1[0] < name2[0]) 
    || (name3[0] < name2[0] && name2[0] < name1[0]))
    {valueOutput(name1, name2, name3);}
    else{
        return 0;
    }

}

My input was: Steinbeck Hemingway Fitzgerald

but the output is the exactly in the same order. I want to sort them alphabetically.

Answer 1

I know that strings are just arrays of char so there should be a method to get the first index.

It seems you mean string literals.

If you have three declarations like these

char *s1 = "Onur";
char *s2 = "Ozbek";
char *s3 = "Hello";

then you can compare first characters of the string literals the following ways

if ( s1[0] == s2[0] )

or

if ( *s2 == *s3 )

The same expressions can be used if instead of pointers you declared arrays

char s1[] = "Onur";
char s2[] = "Ozbek";
char s3[] = "Hello";

In fact you can even use the following expressions

if ( "Onur"[0] == "Ozbek"[0] )

or

if ( *"Onur" == *"Ozbek" )

or even like

if ( 0["Onur"] == 0["Ozbek"] )

to compare first characters of string literals directly.

Answer 2

You can get a particular position using operator[indexNumber]

But if you want to sort, you should use std::sort from #include <algorithm> with a vector of strings std::vector<std::string>

//EDIT: note that a and A are different for a sorting or comparation, search ascii table

I will put a code example do not read further if you do not want the solution

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

int main()
{
  std::vector<std::string> stringArray;
  stringArray.reserve(4);
  stringArray.push_back("Hi");
  stringArray.push_back("Hello world");
  stringArray.push_back("New c++");
  stringArray.push_back("Animal");
  std::sort(stringArray.begin(), stringArray.end());
  for(auto&a : stringArray)
  {
    std::cout << a << '\n';   
  }

}

Answer 3

#include <iostream>

int main() {
    std::string str1, str2, str3;
    std::cout << "Enter First String  :  ";
    getline(std::cin, str1);
    std::cout << "Enter Second String  :  ";
    getline(std::cin, str2);
    std::cout << "Enter Third String  :  ";
    getline(std::cin, str3);
    // The code is descriptive by itself till now

    // Now we gonna compare each of them.
    if(str1[0] < str2[0]) {  // Once the control flow get inside this if statement that means str1 is smaller than str2
        if (str1[0] < str3[0] && str3[0] < str2[0]) 
            std::cout << str1 << std::endl << str3 << std::endl << str2; // In here we get that str1 is smaller than str3 (and str1 is smaller than str2 as well), so the smallest is str1 and we print that. and then we compared str3 with str 2, if str3 is smaller than str2 then we will print secondly str3 and thirdly str2.
        else if (str1[0] < str3[0] && str2[0] < str3[0])
            std::cout << str1 << std::endl << str2 << std::endl << str3; // Here we get that str1 is smaller than str2 and str3 so we firstly print str1 and then we compared str2 with str3, if str2 is smaller than str3 then we will secondly print str2 and thirdly print str3.
        else
            std::cout << str3 << std::endl << str1 << std::endl << str2; // Now both the conditions mentioned above are wrong that means str3 is smaller than str1 and from the very first condition, we get that str1 is smaller than str2. That means smallest is str3 then str1 then str2 and we printed all of them in this order.
    } else { // else will be executed when str2 will be smaller than str1. So till now we get that str2 is smaller than str1. Now remember that str2 is smaller than str1.
        if (str2[0] < str3[0] && str3[0] < str1[0])
            std::cout << str2 << std::endl << str3 << std::endl << str1; // Now here str2 proved to be smaller than str3 (and we already know that str2 is smaller than str1), So str2 is the smallest and we printed firstly str2. Then we compared str3 with str1, if str3 is smaller than str1 then we will secondly print str3 and thirdly print str1.
        else if (str2[0] < str3[0] && str1[0] < str3[0])
            std::cout << str2 << std::endl << str1 << std::endl << str3;  // Now here str2 proved to be smaller than str3 (and we already know that str2 is smaller than str1), So str2 is the smallest and we printed firstly str2. Then we compared str1 with str3, if str1 is smaller than str3 then we will secondly print str1 and thirdly print str3.
        else
            std::cout << str3 << std::endl << str2 << std::endl << str1; // Now both the above conditions are false that means str3 is smaller than str2 and as we know that str2 is smaller than str1, that means str3 is the smallest, so we firstly printed str3 and then str2 and at last str1.
    }
return 0;
}

This is whole code I think that you can understand it... And if you cant understand any particular line, you can freely ask..

Answer 4

If you are aware of STL container std::vector, this job is much easier. If you are looking for something simple, here it is, hopes that the comments help you to understand.

#include <iostream>
#include <algorithm>
#include <vector>
#include <iterator>
int main()
{
    int size = 3;                 //size of your vector
    std::vector<std::string> vec; //initialize the vec with string type
    vec.reserve(size);            // just to reserve the memory

    // input iterator takes strings from std console-size times-and put it back in to vec
    std::copy_n(std::istream_iterator<std::string>(std::cin), size, back_inserter(vec));

    // this will do your job as per requirement
    std::sort(vec.begin(), vec.end());

    // just to print the result
    std::copy(vec.begin(),vec.end(), std::ostream_iterator<std::string>(std::cout,"\n"));
    return 0;
}

Answer 5

Lets suppose that your strings are named st1 , st2 , st3 and you want to perform the above mentioned operation on them.

A quick way to do it would be using std::vector. You push all string first index values to the vector and then sort it.A clear cut implementation would be something like this :

  vector<char> v;
  v.push_back(st1[0]);
  v.push_back(st2[0]);
  v.push_back(st3[0]);

  sort(v.begin() , v.end());

You can read more about vectors here : https://www.geeksforgeeks.org/vector-in-cpp-stl/

Answer 6

If you don't want the code, I'll just tell you the logic to do the same.

1. Hashing

You can use hashing to sort your strings. The idea behind this is that at the position of the first character of your (i)th string you store i. For eg: consider your strings are as follows :: aaa, bbb, ccc

Now at position [ith_string[0] - 'a'] you store i (here 0 position corresponds to 'a', 1 position corresponds to 'b',.. and so on).

In other words you do this array[str1[0] - 'a'] = 1, and so on for every string.

So your array will look like this :: array = {1, 2, 3}

Then you can just print the string using the position you stored in our hashing array. I know this seems a bit difficult, but I would suggest you see some tutorials about hashing, you'll understand it then.

2. Sorting

You can also use sorting, but then you need to store the location of your string. You can use pair to store the string and the location of your string. Then you can use @VaradBhatnagar's solution to sort the strings and depending on the position, you can print it in that order.

In case you're wondering what I just said, please see the below code for reference. I'm sure you'll understand this.(If you don't please feel free to ask doubts).

#include <bits/stdc++.h>
using namespace std;
void hashing(string str[], int n){
    int arr[26] = {0}; // Because there are only 26 alphabets
    for(int i = 0 ; i < n ; i++){
        arr[str[i][0] - 'a'] = i + 1; // we should not store 0, as 0 defines "there was no string starting from this alphaber" 
    }
    for(int i = 0 ; i < n ; i++){
        if(arr[i] != 0){
            cout << str[arr[i] - 1] << endl;
        }
    }
}   
void sorting(string str[], int n){
    std::vector<pair <char, int> > v;
    for (int i = 0 ; i < n ; i++){
        v.push_back(make_pair(str[i][0], i));
    }
    sort(v.begin(), v.end()); // this will sort on the basis of 1st argument in our pair
    for(int i = 0 ; i < n ; i++){
        cout << str[v[i].second] << endl;
    }
}
int main(int argc, char const *argv[])
{
    int n;
    string str[30]; // it can not be larger than 26, because of the question
    cin >> n;
    for(int i = 0 ; i < n ; i++){
        cin >> str[i];
    }
    cout << "Result of hashing" << endl;
    hashing(str, n);

    cout << "Result of sorting" << endl;
    sorting(str, n);

    return 0;
}

Input

3
cccc
bb  
aaaa 

Output

Result of hashing
aaaa
bb
cccc
Result of sorting
aaaa
bb
cccc

Answer 7

Figured it out. I basically had to call the function at each if statement:

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

void valueOutput(string firstName, string secondName, string thirdName){
    cout << "\n";
    cout << firstName << endl;
    cout << secondName << endl;
    cout << thirdName << endl;
}

int main(){
    string name1, name2, name3;

    cout<<"Enter 3 names: "<<endl;

    cin>>name1;
    cin>>name2;
    cin>>name3;

    if(name1[0] < name2[0] && name2[0] < name3[0]){
        valueOutput(name1, name2, name3);
    }
    else if(name1[0] < name3[0] && name3[0] < name2[0]){
        valueOutput(name1, name3, name2);
    }
    else if(name2[0] < name1[0] && name1[0] < name3[0]){
        valueOutput(name2, name1, name3);
    }
    else if(name2[0] < name3[0] && name3[0] < name1[0]){
        valueOutput(name2, name3, name1);
    }
    else if(name3[0] < name1[0] && name1[0] < name2[0]){
        valueOutput(name3, name1, name2);
    } 
    else if(name3[0] < name2[0] && name2[0] < name1[0]){
        valueOutput(name3, name2, name1);
    }

}

Answer 8

enter image description hereLets suppose your 3 names is name1 and name2 and name3 and you know that string is just an array of char so you can compare each char using its Ascii number and dont forget to take in consideration the capital and small letters as the difference between them in ascii is 32 and small litters is greater than capital letters so you will convert between them as in code. there isn't any complex function here so it's so easy to understand

#include <iostream>
using namespace std;

void comparing(string& name1,string& name2);
void comparing(string& name1,string& name2,string& name3);

int main(){
    string name1, name2, name3;
    cout<<"Enter 3 names: "<<endl;
    cin>>name1;
    cin>>name2;
    cin>>name3;
    comparing(name1,name2,name3);
}
void comparing(string& name1,string& name2)
{
    string t;
    for(int i=0;i<name1.size();i++){
        int x = (int)name1[i];
        int y = (int)name2[i];
        if(x<=97 && x>=122){
            x=x-32;
        }
        if(y<=97 && y>=122){
            y=y-32;
        }
        if(x>y){
            t=name1;
            name1=name2;
            name2=t;
            break;
        }}
}
void comparing(string& name1,string& name2,string& name3)
{
    comparing(name1,name2);
    comparing(name2,name3);
    comparing(name1,name3);
    comparing(name1,name2);
    cout << name1 << " " <<name2 << " " <<name3 <<endl;
}