c++ char array input - explanation

Question

I have an exercise to write a program that receives a sentence and then takes from each word the first letter and creates a new word.

My code:

int main(){

char* str = new char[50];

for (int i = 0; i < 50; i++)
    str[i] = NULL;

cin >> str; 

cout<<str;

for (int i = 0; i < 50; i++) 
    cout << str[i]; 


system("pause");
return 0;
}

But when I want to print the sentence it prints only the first word.

input: 
abcdef abc des

output: 
abcdef abc des
abcdef *******************************************

And when I press a space what goes into the array? How can I know when I'm running on the array with the FOR loop When do I get to the Character where there is space?

@Liran Use function std::getline( std::cin, str ). The operator >> reads until a white space is encountered. Also it is not clear why the array is allocated dynamically. — Vlad from Moscow, Mar 27 '17 at 09:23
And please learn how to use [`std::string`](http://en.cppreference.com/w/cpp/string/basic_string). — Some programmer dude, Mar 27 '17 at 09:23
If all you're doing is reading words, gathering their first characters of each along the way to assemble a new word, and then reporting that word as your result, [why not just do **that**](http://ideone.com/Z9mrDb). Or did I miss something. — WhozCraig, Mar 27 '17 at 09:31
Can use this link for reference "http://stackoverflow.com/questions/15362367/how-to-read-the-whole-lines-from-a-file-with-spaces" — Santosh Sahu, Mar 27 '17 at 09:40

jpo38 · Answer 1 · 2017-03-27T09:30:27.650

3

cin >> str; stops when it finds a space character.

use this to read the whole line:

std::string myStr;
std::getline( std::cin, myStr);

Note: You'll have to include <string>

edited Mar 27 '17 at 09:30

answered Mar 27 '17 at 09:23

jpo38

20,821
10
70
151

Is this dynamic allocation of a string? Because I need a dynamic allocation. – Liran Mar 27 '17 at 09:32
@Liran - Let `std::string` worry about the resource management, that's what it's for. – StoryTeller - Unslander Monica Mar 27 '17 at 09:47
@Liran: Yes, std::string definitely uses dynamic allocation. – jpo38 Mar 27 '17 at 10:12
@jpo38: if i have string* str, how i can find the length of str? – Liran Mar 27 '17 at 10:58
`std::string str="hello"; str.size(); //return 5` – Adrian Maire Mar 27 '17 at 11:05
@Liran: Have you searched? Check the doc: http://www.cplusplus.com/reference/string/string/ – jpo38 Mar 27 '17 at 11:10

score 0 · Answer 2 · answered Mar 27 '17 at 10:31

A command input is supposed to contain several parameters separated by spaces. For this reason, std::cin follows the same semantic and divide inputs by spaces.

WRITE YOUR INPUTS:
> hello world

Is considered by std::cin as 2 inputs.

input1: hello
input2: world

You may call std::cin several times to get them:

std::string str1, str2, str;
std::cin >> str1;
std::cin >> str2;
str = str1 + " " + str2;

Obviously and in most of the cases, we do not know how many words the user input, and calling std::cin several times make the program to block for a new input.

As an alternative, getline allows to get a single input:

std::string str;
std::getline(std::cin, str);

c++ char array input - explanation

2 Answers2

Linked

Related