Trying to make string array passed through methods C++ - c++

Question

I'm trying to read names and ages from user, until user inputs "stop". Then just print all these values. Please help me , I'm just the beginner in C++
// Pass.cpp
// Reading names and ages from user and outputting them
#include <iostream>
#include <iomanip>
#include <cstring>
using std::cout;
using std::cin;
using std::endl;
using std::setw;
using std::strcmp;
char** larger(char** arr);
int* larger(int* arr);
void read_data(char*** names, int** ages);
void print_data(char*** names, int** ages);
int main()
{
char** names = new char*[5];
char*** p_names = &names;
int* ages = new int[5];
int** p_ages = &ages;
read_data(p_names,p_ages);
print_data(p_names,p_ages);
}
void read_data(char*** names, int** ages)
{
const char* sent = "stop";
const int MAX = 15;
int count = 0;
char UI[MAX];
cout << "Enter names and ages."
<< endl << "Maximum length of name is " << MAX
<< endl << "When stop enter \"" << sent << "\".";
while (true)
{
cout << endl << "Name: ";
cin.getline(UI,MAX,'\n');
if (!strcmp(UI, sent))
break;
if (count + 1 > sizeof (&ages) / sizeof (&ages[0]))
{
*names = larger(*names);
*ages = larger(*ages);
}
*names[count] = UI;
cout << endl << "Age: ";
cin >> *ages[count++];
}
}
void print_data(char*** names, int** ages)
{
for (int i = 0; i < sizeof(*ages) / sizeof(*ages[0]);i++)
{
cout << endl << setw(10) << "Name: " << *names[i]
<< setw(10) << "Age: " << *ages[i];
}
}
char** larger(char** names)
{
const int size = sizeof(names) / sizeof(*names);
char** new_arr = new char*[2*size];
for (int i = 0; i < size; i++)
new_arr[i] = names[i];
return new_arr;
}
int* larger(int* ages)
{
const int size = sizeof(ages) / sizeof(*ages);
int* new_arr = new int[2 * size];
for (int i = 0; i < size; i++)
new_arr[i] = ages[i];
return new_arr;
}

Answer 1

You are really over complicating things.
Given the original problem:
Write a program that reads a number (an integer) and a name (less than
15 characters) from the keyboard. Design the program so that the data
is done in one function, and the output in another. Store the data in
the main() function. The program should end when zero is entered for
the number. Think about how you are going to pass the data between
functions
The problem wants you to think about passing parameters to functions. A simple solution would be:
#include "stdafx.h"
#include <iostream>
#include <iomanip>
using namespace std;
// Pass in a char array and an integer reference.
// These values will be modified in the function
void read_data(char name[], int& age)
{
cout << endl << "Age: ";
cin >> age;
cin.ignore();
cout << endl << "Name: ";
cin.getline(name, 16);
}
// Pass a const array and an int value
// These values will not be modified
void print_data(char const *name, int age)
{
cout << endl << setw(10) << "Name: " << name
<< setw(10) << "Age: " << age;
}
int main()
{
char name[16];
int age;
cout << "Enter names and ages."
<< endl << "Enter 0 age to quit.";
do {
read_data(name, age);
print_data(name, age);
} while (0 != age)
}
EDIT: Modified per user3290289's comment
EDIT2: Storing data in an array
// Simplify by storing data in a struct (so we don't have to manage 2 arrays)
struct Person {
char name[16];
int age;
};
// Returns how many People were input
int read_data(Person*& arr)
{
int block = 10; // How many persons to allocate at a time
arr = NULL;
int arr_size = 0;
int index = 0;
while (true) {
if (index == arr_size) {
arr_size += block;
arr = (Person *)realloc(arr, arr_size * sizeof(Person)); // Reallocation
// Should check for error here!
}
cout << endl << "Age: ";
cin >> arr[index].age;
cin.ignore();
if (0 == arr[index].age) {
return index;
}
cout << endl << "Name: ";
cin.getline(arr[index++].name, 16);
}
}
void print_data(Person *arr, int count)
{
for (int i = 0; i < count; i++) {
cout << endl << setw(10) << "Name: " << arr[i].name
<< setw(10) << "Age: " << arr[i].age;
}
}
int main()
{
Person *arr;
int count = read_data(arr);
print_data(arr, count);
free(arr); // Free the memory
}

Answer 2

try this:
#include <iostream>
#include <iomanip>
#include <vector>
#include <sstream>
using std::cout;
using std::cin;
using std::endl;
using std::setw;
using std::strcmp;
void read_data(std::vector<std::string> &names, std::vector<int> &ages);
void print_data(std::vector<std::string> &names, std::vector<int> &ages);
int main()
{
std::vector<std::string> names;
std::vector<int> ages;
read_data(names, ages);
print_data(names, ages);
}
void read_data(std::vector<std::string> &names, std::vector<int> &ages)
{
const char* sent = "stop";
cout << "Enter names and ages."
<< endl << "When stop enter \"" << sent << "\".";
while (true)
{
std::string input;
cout << endl << "Name: ";
std::getline(cin, input);
if (!strcmp(input.c_str(), sent))
break;
names.push_back(input);
cout << endl << "Age: ";
std::string age;
std::getline(cin, age);
ages.push_back(atoi(age.c_str()));
}
}
void print_data(std::vector<std::string> &names, std::vector<int> &ages)
{
for (int i = 0; i < names.capacity() ; i++)
{
cout << endl << setw(10) << "Name: " << names.at(i)
<< setw(10) << "Age: " << ages.at(i);
}
}

Answer 3

One problem I see is this if statement:
if (count + 1 > sizeof (&ages) / sizeof (&ages[0]))
&ages is the address of an int**, a pointer, and so it's size is 8 (usually) as that is the size of a pointer type. The function does not know the size of the array, sizeof will only return the correct answer when ages is declared in the same scope.
sizeof(&ages) / sizeof(&ages[0])
will always return 1

Answer 4

I believe one natural solution about this problem is as follows:
create a "std::map" instance. Here std::map would sort the elements according to the age. Here my assumption is after storing the data into the container, you would like to find about a particular student age/smallest/largest and all various manipulation with data.Just storing and printing the data does not make much sense in general.
create a "std::pair" and take the both input from the user into the std::pair "first" and "second" member respectively. Now you can insert this "std::pair" instance value into the above "std::map" object.
While printing, you can now fetch the each element of "std::map" in the form of "std::pair" and then you can display pair "first" and "second" part respectively.