Ok guys, i'm very beginner and trying to enter string to a char array using pointers..and then display what i've written.
There're two things i want to ask about. First , if i didn't want to specify a size for the array and just want it to expand to contain all string i've entered ..how is that ?
And second after i enter the string and display it...it won't contain the SPACE between word...
like if i entered "i love cookies"...it will be displayed as "ilovecookies"..So how to solve that ?
Here's my little code ...
#include <iostream>
using namespace std;
int main()
{
char *strP , str[100] ;
strP = str ;
for(int i =0 ; i<10 ; i++) cin >> *(strP+i) ;
for(int i =0 ; i<10 ; i++) cout << *(strP+i) ;
return 0;
}
sorry for my silly questions, I'm beginner to this language as said and don't want to miss things before moving on .
Thanks in advance .
1) You need to either use a string object or new if you want to dynamically resize your string.
2) It doesn't contain the spaces because cin reads one words at a time. There are several ways to get around this. The one I would use is switch to using scanf and printf instead of cin and cout. Or, as vivin said, you can use getchar()
EDIT: grammar
cin always stops when it encounters a space. If you're entering character by character, try using getchar().
Arrays can't change their size. You should use std::vector<char>, or even better for strings you would use std::string.
Related
I'll preface this by saying I'm relatively new to posting questions, as well as C++ in general, my title is a little lame as it doesn't really specifically address the problem I am dealing with, however I couldn't really think of another way to word it, so any suggestions on improving the title is appreciated.
I am working on a relatively simple function which is supposed to get a string using getline, and read the spaces and/or newlines in the string so that it can output how many words have been entered. After reaching the character 'q' it's basically supposed to stop reading in characters.
void ReadStdIn2() {
std::string userInput;
const char *inputArray = userInput.c_str();
int count = 0;
getline(std::cin, userInput, 'q');
for (int i = 0; i < strlen(inputArray); i++){
if ((inputArray[i] == ' ') || (inputArray[i] == '\n')){
count += 1;
}
}
std::cout << count << std::endl;
}
I want to be able to enter multiple words, followed by newlines, and have the function accurately display my number of words. I can't figure out why but for some reason after entering 3 newlines my count goes right back to 0.
For example, if I enter:
hello
jim
tim
q
the function works just fine, and returns 3 just like I expect it to. But if I enter
hello
jim
tim
bill
q
the count goes right to 0. I'm assuming this has something to do with my if statement but I'm really lost as to what is wrong, especially since it works fine up until the 3rd newline. Any help is appreciated
The behaviour of the program is undefined. Reading input into std::string potentially causes its capacity to increase. This causes pointers into the string to become invalid. Pointers such as inputArray. You then later attempt to read through the invalid pointer.
P.S. calculating the length of the string with std::strlen in every iteration of the loop is not a good idea. It is possible to get the size without calculation by using userInput.size().
To fix both issues, simply don't use inputArray. You don't need it:
for (int i = 0; i < userInput.size(); i++){
if ((userInput[i] == ' ') || (userInput[i] == '\n')){
...
i want to use the word i insert to use it to make comparison in if condition to show some word it the comparison is true.
here is my code
#include <iostream>
using namespace std;
int main()
{
char u[5];
cout<<" p " <<" c "<<" U "<<endl;
cout<<" pepsi=5"<<" coca=3"<<" 7-UP=2"<<endl;
cout<<"CHOOSE your drink"<<endl;
cin>>u;
if (u=="pepsi")
cout<<"your choice is pepsi and ur bill is 5 ";
}
First in the future I would suggest trying to be more specific on what your problem is and what you don't understand. Just saying I want to do X and here is my code is giving us very little to work with and we are basically just guessing on what you are having problems with.
Now on to what I believe you are having problems with (I am assuming since you didn't tell us what is going wrong).
In this case you are using a character array with a length of 5. Now when you use character arrays you need to take into account that all the reasonable inputs that that variable might store will actually fit into that character array.
Let's look at pepsi. You might think it would fit but in fact it doesn't because you are forgetting about the null character that is added on the end. This is what it looks like.
u[0] = 'p'
u[1] = 'e'
u[2] = 'p'
u[3] = 's'
u[4] = 'i'
u[5] = '\0'
So as you can see there is actually 6 characters in this word which will cause a overflow. I am assuming this is your problem.
Now how do we fix this? As others have said in the comments if you are using C++ it is probably better for you to use std::string for this problem since it will hide from you most of the problems you have to do deal with when using C style string (What you are using now). Then once you feel more comfortable with the language you can come back and revisit C style strings.
With std::string it would look something like this. Remember that when testing strings case matters (IE "string" is not the same as "String").
std::string choice;
std::cin >> choice;
if (choice == "pepsi")
{
std::cout << "You selected pepsi!" << std::endl;
}
Hope that helps a little and fixes your problems.
Ok, just to be up front, this IS homework, but it isn't due for another week, and I'm not entirely sure the final details of the assignment. Long story short, without knowing what concepts he'll introduce in class, I decided to take a crack at the assignment, but I've run into a problem. Part of what I need to do for the homework is read individual characters from an input file, and then, given the character's position within its containing word, repeat the character across the screen. The problem I'm having is, the words in the text file are single words, each on a different line in the file. Since I'm not sure we'll get to use <string> for this assignment, I was wondering if there is any way to identify the end of the line without using <string>.
Right now, I'm using a simple ifstream fin; to pull the chars out. I just can't figure out how to get it to recognize the end of one word and the beginning of another. For the sake of including code, the following is all that I've got so far. I was hoping it would display some sort of endl character, but it just prints all the words out run together style.
ifstream fin;
char charIn;
fin.open("Animals.dat");
fin >> charIn;
while(!fin.eof()){
cout << charIn;
fin >> charIn;
}
A few things I forgot to include originally:
I must process each character as it is input (my loop to print it out needs to run before I read in the next char and increase my counter). Also, the length of the words in 'Animals.dat' vary which keeps me from being able to just set a number of iterations. We also haven't covered fin.get() or .getline() so those are off limits as well.
Honestly, I can't imagine this is impossible, but given the restraints, if it is, I'm not too upset. I mostly thought it was a fun problem to sit on for a while.
Why not use an array of chars? You can try it as follow:
#define MAX_WORD_NUM 20
#define MAX_STR_LEN 40 //I think 40 is big enough to hold one word.
char words[MAX_WROD_NUM][MAX_STR_LEN];
Then you can input a word to the words.
cin >> words[i];
The >> operator ignores whitespace, so you'll never get the newline character. You can use c-strings (arrays of characters) even if the <string> class is not allowed:
ifstream fin;
char animal[64];
fin.open("Animals.dat");
while(fin >> animal) {
cout << animal << endl;
}
When reading characters from a c-string (which is what animal is above), the last character is always 0, sometimes represented '\0' or NULL. This is what you check for when iterating over characters in a word. For example:
c = animal[0];
for(int i = 1; c != 0 && i < 64; i++)
{
// do something with c
c = animal[i];
}
Whenever I input a variable using cin, after one hits enter it automatically goes to a new line. I'm curious if there's a way to use cin without having it go to a new line. I'm wanting to cin and cout multiple things on the same line in the command prompt. Is this possible?
You can't use cin or any other standard input for this. But it is certainly possible to get the effect you are going for. I see you're on Windows using Visual Studio, so you can use, for example, _getch. Here's an example that reads until the next whitespace and stores the result in a string.
#include <conio.h> // for _getch
std::string get_word()
{
std::string word;
char c = _getch();
while (!std::isspace(c))
{
word.push_back(c);
std::cout << c;
c = _getch();
}
std::cout << c;
return word;
}
It's not very good. For example, it doesn't handle non printing character input very well. But it should give you an idea of what you need to do. You might also be interested in the Windows API keyboard functions.
If you want a wider audience, you will want to look into some cross-platform libraries, like SFML or SDL.
you can also use space for input instead of enter
something like this:
cin >> a >> b >> c;
and in input you type
10 20 30
then
a=10
b=20
c=30
As others have noted, you can't do this with cin, but you could do it with getchar(). What you would have to do is:
collect each character individually using getchar() (adding each to the end of a string as it is read in, for instance), then
after reading each character, decide when you've reached the end of one variable's value (e.g. by detecting one or more ' ' characters in the input, if you're reading in int or double values), then
if you've reached the end of the text for a variable, convert the string of characters that you've built into a variable of the appropriate type (e.g. int, double, etc.), then
output any content onto the line that might be required, and then
continue for the next variable that you're reading in.
Handling errors robustly would be complicated so I haven't written any code for this, but you can see the approach that you could use.
I don't think what you want to do can be achieved with cin. What you can do is to write all your input in one line, with a delimiter of your choosing, and parse the input string.
It is not possible. To quote #Bo Persson, it's not something controlled by C++, but rather the console window.
I can't comment but if you leave spaces between integers then you can get the desired effect. This works with cin too.
int a, b, c;
cin>>a; cin>>b; cin>>c;
If you enter your values as 10 20 30 then they will get stored in a, b, and c respectively.
just use the gotoxy statement. you can press 'enter' and input values in the same line
for eg. in the input of a 3*3 matrix:
#include<iostream.h>
#include<conio.h>
void main()
{clrscr();
int a[20][20],x,y;
cout<<"Enter the matrix:\n ";
for(int r=2;r<7;r+=2)
for(int c=2;c<7;c+=2)
{gotoxy(c,r);
cin>>a[r][c];
}
getch();}
Now, I am facing with such a problem: Compare two strings without using "strcmp" in library function.
I have defined the function "mystrcmp" correctly, but I also have to put the string entered into a character array. How can I realize it?
Here is my wrong codes:
char a1[100],a2[100];
int j=0;
do
{
cin>>a1[j];
j=j+1;
}while(getchar()!=10);
int k=0;
do
{
cin>>a2[k];
k=k+1;
}while(getchar()!=10);
cout<<j<<" "<<k<<"\n";
I want to see if the loops are correct through j and k. Unfortunately, the results are wrong.
For example, when I enter "abcdefg" and "gfedcba", I get the result "j=4, k=4".
What's wrong with my codes? How can I correct it?
I'm looking forward to your answers. Thank you.
Why are you using the value 10 in your code? Don't use integer literals in place of character constants, because when you attempt to run this code on a computer that uses the EBCDIC character set you'll notice that '\n' has the value 37, not 10. Use '\n' instead of 10.
Don't mix getchar and cin code. That's a pretty bad idea, because they both consume one character each. In other words, getchar() is consuming one byte, and cin is consuming one byte, so you're consuming two bytes per loop and only storing one of those bytes. If you're going to use getchar, I think you mean something like this:
for (int c = getchar(); c >= 0 && c != '\n'; c = getchar()) {
a1[j++] = c;
}
a1[j] = '\0';
The same sort of thing using C++'s cin:
for (int c = cin.get(); cin.good() && c != '\n'; c = cin.get()) {
a1[j++] = c;
}
a1[j] = '\0';
This is dangerous code. You can write out of a1 & a2 bounds. Use functions made for this, for example cin.getline
http://www.cplusplus.com/reference/istream/istream/getline/