First off, this is a "homework" question so vector libraries and string libraries are off limits. I'm trying to get to the basics of c++.
My intention with this code is to make and use an array of string arrays. A list of words in other words.
When I run this code I get a bunch of nonsense.
If there is a better way to make a list of words in c++, I would love to hear about it.
const int cart_length = 50;
const int word_length = 50;
int main()
{
char cart_of_names[cart_length][word_length];
float cart_of_costs[cart_length];
char name[word_length];
cout << "enter the name of the first item: ";
cin >> name;
for(int i=0; i<word_length; i++)
{
cart_of_names[0][i] = name[i];
}
cout << endl;
cout << "that is: ";
for(int x=0; x<word_length; x++)
{
cout << cart_of_names[0][x];
}
cout << endl;
return 0;
}
If the string entered is not 50 characters long (cart_length), then less than 50 characters will be valid in the name. You should have an if(cart_of_names[0][x]==0) break; in your second loop.
I don't exactly understand what you are looking for. Following code will help you to read and print a list of 50 words. Hope this would help you.
const int cart_length = 50;
const int word_length = 50;
int main()
{
char cart_of_names[cart_length][word_length];
float cart_of_costs[cart_length];
for(int i=0; i<cart_length; i++)
{
cout << "enter the name of the " << i + 1 << "th item: ";
cin >> cart_of_names[i];
}
cout << "that is: ";
for(int x=0; x < cart_length; x++)
{
cout << cart_of_names[x] << endl;
}
return 0;
}
Check out STLSoft's fixed_array_2d (and it's higher order siblings). There's a detailed discussion of how they're implemented for maximum performance in Matthew Wilson's Imperfect C++.
If you can't use std::string, at least look at the functions like strncpy() from C for your name copying. Also, you're forgetting that c-style strings are null terminated.
Unless you're forbidden to use STL (which would be just mean), just use std::list<std::string>. www.cplusplus.com has detailed descriptions and examples for those classes.
Otherwise, you're stuck with an array of char arrays: in that case, be prepared for a lot of buffer overflow errors. Look around on the above site for the char[] management functions (strncpy() and the like), they'll make your life a bit easier (but not a lot).
In C, the best way I found to conceptualize what you are trying to do is using an array of char*. Same effect, but if you start to work with it I believe you may find it is easier on the brain.
It looks pretty close to me. Strings in C are null-terminated, which means that the end of the string is indicated by a null character. In a sense, a string in C is really just an array of bytes.
When you do:
cout << "enter the name of the first item: ";
cin >> name;
If I enter the string "Book", in memory it'll look like something like:
|0|1|2|3|4|5..49|
|B|o|o|k|0|*HERE BE DRAGONS*
Well, really it will contain the ASCII values corresponding to those letters, but for our purposes, it contains those letters. There here be dragons is memory that that you didn't initialize, so it contains whatever garbage your platform sets it to.
So when you copy your string, you need to instead look for that 0 byte at the end of the string.
for(int i=0; name[i]!=0; i++)
{
cart_of_names[0][i] = name[i];
}
Then when you output it, you don't actually need to do it a character at a time. You can just do cout<<cart_of_names[0]. cout knows where the string ends because of that terminating null character.
If you use strcpy() instead of
cart_of_names[0][i] = name[i];
it may work better but I cringe just looking at all that code.
"If there is a better way to make a list of words in c++, I would love to hear about it."
Include #include <string> and use std::string. The std::string type is part of the C++ specification, I think.
#include <iostream>
#include <string>
int main(void) {
std::string list[7];
list[0] = "In C++";
list[1] = "you can use";
list[2] = "the `std::string` type.";
list[3] = "It removes";
list[4] = "many of the problems";
list[5] = "introduced by";
list[6] = "C-style strings.";
for (int k=0; k<7; k++) std::cout << list[k] << ' ';
std::cout << '\n';
return 0;
}
Related
So I am still new to C++, and I'm trying to make a program that has the user input a string, and then my functions return the string in reverse case, all lower case, and then all uppercase. Instead I just keep receiving the first letter of the string back, always uppercase. Not sure what I am doing wrong. Any suggestions?
#include <iostream>
#include <string>
#include <cstring>
using namespace std;
char answer[255] = "";
int max = strlen(answer);
void reverse() {
for (int i = 0; i < max; i++) {
if (islower(answer[i])) {
isupper(answer[i]);
}
else if (isupper(answer[i])) {
islower(answer[i]);
}
else if (isspace(answer[i])) {
isspace(answer[i]);
}
}
cout << answer[max];
}
void lower() {
for (int i = 0; i < max; i++) {
if (isupper(answer[i])) {
islower(answer[i]);
}
else {
answer[i] = answer[i];
}
}
cout << answer[max];
}
void upper() {
for (int i = 0; i < max; i++) {
if (islower(answer[i])) {
isupper(answer[i]);
}
else {
answer[i] = answer[i];
}
}
cout << answer[max];
}
int main() {
cout << "Please enter a word, or a series of words: " << endl;
cin >> answer[max];
reverse();
lower();
upper();
system("pause");
return 0;
}
islower(char) is just a built in function to check if the char is in lowercase or not. Same goes with isupper. It does not change the case of the character.
In order to convert to lowercase/uppercase, use tolower/toupper. This would return the character in the converted case. But, it is important that you need to assign the returned value to the character itself.
Refer to this answer for some more clarity related to islower, isupper, tolower and toupper.
And now coming to the point why it's printing just the 1st character: As #user4581301 has mentioned in his comment,
"cin >> answer[max]; will read exactly one character because answer[max] is exactly one character, the first character. In C++ you have to do things in order. For example, int max = strlen(answer); will provide an answer based on what is in that string at that time. Since the string was initialized one line earlier and contains an empty string, max will be 0."
Hence your cin should be cin >> answer. BUT, this will accept the 1st word of your sentence. In order to accept all the words including the spaces, use getline() instead. And for using this, answer should be declared as string answer instead of a char array.
This is how you accept a full sentence: getline(cin,answer);
And your variable max will give an error in a few compilers as being ambiguous. This is because of the using namespace std;. to avoid this, rename max to something else, like maxlen.
And finding the length of answer: It would be better if you call answer.length() after accepting the string from user rather than doing it globally.
Your working code should look something like this:
#include <iostream>
#include <string>
#include <cstring>
using namespace std;
string answer;
int maxlen;
void reverse() {
for (int i = 0; i < maxlen; i++) {
if (islower(answer[i])) {
answer[i] = toupper(answer[i]);
}
else if (isupper(answer[i])) {
answer[i] = tolower(answer[i]);
}
else if (isspace(answer[i])) {
answer[i]=' ';
}
}
cout << "Reversed string: " + answer << endl;
}
void lower() {
for (int i = 0; i < maxlen; i++) {
if (isupper(answer[i])) {
answer[i] = tolower(answer[i]);
}
else {
answer[i] = answer[i];
}
}
cout << "Lower case string: " + answer << endl;
}
void upper() {
for (int i = 0; i < maxlen; i++) {
if (islower(answer[i])) {
answer[i] = toupper(answer[i]);
}
else {
answer[i] = answer[i];
}
}
cout << "Upper case string: " + answer << endl;
}
int main() {
cout << "Please enter a word, or a series of words: " << endl;
getline(cin,answer);
cout << "Original string: " + answer << endl;
maxlen = answer.length();
reverse();
lower();
upper();
return 0;
}
With the output:
Please enter a word, or a series of words:
ReVeRsAl UPPER aNd lower
Original string: ReVeRsAl UPPER aNd lower
Reversed string: rEvErSaL upper AnD LOWER
Lower case string: reversal upper and lower
Upper case string: REVERSAL UPPER AND LOWER
cin >> answer[max];
will read exactly one character because answer[max] is exactly one character, the character in the array at position max.
max is 0 because you have to do things in order. For example,
int max = strlen(answer);
will provide the length of answer at that time this line is reached. Since the string was initialized one line earlier
char answer[255] = "";
and contains an empty string, max will be 0. This means answer[max] is answer[0] Nothing in the code ever changes max, so it will remain 0.
OK, say we change things a little and rather than reading into a single character, we read into answer as a string. You will need to
cin.getline(answer, sizeof(answer));
because
cin >> answer;
will read one whitespace-delimited token. One word. Your stated goal is to read more than one word. istream::getline will read everything it finds into the first parameter up to the end of the line or it finds the number of characters specified in the second parameter minus 1 (in order to reserve space for the string's null terminator). sizeof(answer) is literally the size of the answer array in bytes. We're operating in byte-sized characters so the count of characters and number of bytes are the same. Extra care must be taken if multibyte characters are being used.
This seems like a good place to recommend using std::string and std::getline instead. They make a large number of problems, such as the maximum number of characters that can be read, vanish for the vast majority of cases.
I'm not going to use them here, though because the assignment likely has a "No strings" policy.
So now that we have cin.getline(answer, sizeof(answer)); reading the user's input we can work on getting the size for max. We could strlen, but we could also use istream::gcount to get the number of characters read by getline.
main now looks something like
int main() {
cout << "Please enter a word, or a series of words: " << endl;
cin.getline(answer, sizeof(answer));
max = cin.gcount();
reverse();
lower();
upper();
system("pause");
return 0;
}
Whole bunch of stuff can go wrong at this point.
using namespace std; can wreak havoc on the max because of possible collisions with std::max. In general, avoid using namespace std; The few letters it saves you from typing often are recovered by the time wasted debugging the weird errors it can introduce.
isupper(answer[i]); doesn't do anything useful as others have noted in the comments. You want
answer[i] = toupper(static_cast<unsigned char>(answer[i]));
See Do I need to cast to unsigned char before calling toupper(), tolower(), et al.? for why that insane-and-pointless-looking cast may be necessary. Thank you HolyBlackCat for bringing that to my attention.
Self assignments like
answer[i] = answer[i];
are pointless for reasons that should be obvious once you stop and think about it.
Likewise
else if (isspace(answer[i])) {
isspace(answer[i]);
}
May not be particularly useful. If answer[i] is a space, set it to a space? It's already a space. What it would do is replace other forms of whitespace, tabs and carriage returns, with a space. Newline has already been picked off by getline. Also probably needs a cast similar to the one used in the toupper example above. I'm still reading up on that.
As hinted at above,
cout << answer[max];
is not effective. It prints out one character, and if max has been fixed, answer[max] will be the terminating null. Instead print out the whole array.
cout << answer;
General suggestions:
Don't write much code at a time. Write a few lines, a function at the most, before compiling and testing. If you had tested
int main() {
cout << "Please enter a word, or a series of words: " << endl;
cin >> answer[max];
cout << answer;
}
You would have immediately seen data was not being read correctly. and fixed it before proceeding. By allowing errors to build up, you make it harder to find any one bug. You may correctly fix a bug only to find the fix undone or concealed by another bug.
Avoid using global variables. Try to place variables in the smallest possible scope. In this case, move answer and max into main and pass them to the other functions as parameters. This makes it a lot easier to keep track of who set what variable and when. It also helps prevent accidental Variable Shadowing.
I am basically trying to store everything after a certain index in the array.
For example, I want to store a name which is declared as char name[10]. If the user inputs in say 15 characters, it will ignore the first five characters and store the rest in the char array, however, my program crashes.
This is my code
char name[10];
cout<< "Starting position:" << endl;
cin >> startPos;
for(int i= startPos; i< startPos+10; i++)
{
cout << i << endl; // THIS WORKS
cout << i-startPos << endl; // THIS WORKS
name[i-startPos] = name[i]; // THIS CRASHES
}
For example, if my name was McStevesonse, I want the program to just store everything from the 3rd position, so the end result is Stevesonse
I would really appreciate it if someone could help me fix this crash.
Thanks
Suppose i is equal to 3. In the last iteration of the loop, i is now equal to 12, so substituting 12 in for i, your last line reads
name[12-startPos] = name[12];
name[12] is out of bounds of the array. Based on what you have shown so far, there is nothing but garbage stored in name anyway before you start doing this assignment, so all you're doing is reorganizing garbage in the array.
Please in future: post full compilable example.
A simple answer is that your array maybe is out of bound, since you don't provide full example its hard to know exactly.
Here is a working example:
#include <iostream>
using namespace std;
int main() {
int new_length, startPos;
int length = 15;
char name[15]= "McStevesonse";
cout<< "Starting position:" << endl;
cin >> startPos;
if(new_length <1){ // you need to check for negative or zero value!!!
cout << "max starting point is " <<length-1 << endl;
return -1;
}
new_length=length-startPos;
char newname[new_length];
for(int i= 0; i<new_length; i++){
newname[i] = name[i+startPos]; // THIS CRASHES
}
cout << "old name: " << name << " new name: " << newname << endl;
return 0 ;
}
To put it simply, change this:
for(int i= startPos; i< startPos+10; i++)
To this:
for(int i= startPos; i<10; i++)
You should be fine with that.
Explanation:
At some point, when you use the your old loop, this name[i-startPos] = name[i] would eventually reach an array index out of bounds and causes the crash.
Don't forget to clean up/hide the garbage:
Doing so, would cause the output to produce some kind of garbage outputs. If you got a character array of 'ABCDEFGHIJ', and have chosen 3 as the starting position, the array would be arranged to 'DEFGHIJHIJ'. In your output, you should atleast hide the excess characters, or remove by placing \0's
this script is supposed to output array values that were inputted by the user into array "store." I am trying to store all the char array values into string temp. I get the error on line 12: "[Error] invalid conversion from 'char*' to 'char' [-fpermissive]." Would appreciate any help!
Edit: so I fixed the declaration and now at least it compiles, but the answer I get on my cmd is all jumbled up. Why is this so? The cmd only correctly couts the first string but after the space, it messes up.
#include <iostream>
#include <cstdlib>
using namespace std;
void coutArray(char[], int);
int main()
{
char store[50];
cout << "enter text: " << endl;
cin >> store;
coutArray(store, 50);
system("pause");
return 0;
}
void coutArray(char store[], int max)
{
string temp = "";
int i = 0;
while (i < max)
{
temp += store[i];
i++;
}
cout << temp << endl;
}
Using input from all answerers I finally got the fixed code:
#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;
void coutArray(char[], int);
int main()
{
char store[50] = {0};
cout << "enter text: " << endl;
cin.getline(store, 50);
coutArray(store, 50);
system("pause");
return 0;
}
void coutArray(char store[], int max)
{
string temp = "";
int i = 0;
while (i < max && store[i]!=0)
{
temp += store[i];
i++;
}
cout << temp << endl;
}
Thanks everyone. i learned a lot!!!
When you get an input using "cin" your input automatically ends with 0 (NULL).
You just need to add one little piece of code to your while statement.
instead of this :
while (i < max)
use this :
while (i < max && store[i]!=0)
Now it will stop when the input string is finished and won't print any garbage existed in the array beforehand.
To show that cin does add terminating zero, i initialized the array to 46, and put a breakpoint after the cin
so I fixed the declaration and now at least it compiles, but the answer I get on my cmd is all jumbled up. Why is this so?
Not sure what you mean by jumbled up. But since you did not tell us what you typed its hard to know it looks like it worked to me:
> ./a.out
enter text:
Plop
Plop�ȏU�
Notice that since my input is only 4 characters long. This means that a lot of the characters in the array still have undefined (ie random values). This is why I am seeing junk. To get past this initialize the array to have all 0 values.
char store[50] = {0};
Even bettern use a C++ object than handles longer strings.
std::string store;
std::getline(std::cin, store);
Note: passing arrays to functions by value is not a good idea. On the other end they have decayed to pointers and thus do not act like arrays anymore (they act like pointers whose semantics are similar but not identical).
If you must pass an array pass it by reference. But I would use a C++ container and pass that by reference (it is much safer than using C constructs). Have a look at std::string
The declaration of the function is wrong. Should be void coutArray(char *, int);
Look at the Implicit Conversion rules to understand what the compiler can do and what it cannot to do for you.
The issue with your program was that you were probably entering in less characters than the maximum size of the buffer. Then when you passed the maximum size as the parameter to coutArray, you assigned unfilled slots in the char array to temp. These unfilled slots could contain anything, as you have not filled them up to that point.
Your program is still correct, but what would be better would be to use read so that the number of bytes you specify is the minimum number of bytes that can be entered:
std::cin.read(store, 50);
Even better solution would be to use std::string:
std::string store;
std::cin >> store;
// or for the entire line
std::getline(std::cin, store);
It also follows that your coutArray should be changed to:
void coutArray(std::string);
// ...
void coutArray(std::string str)
{
std::cout << str << std::endl;
}
Look at this way
template<typename T, size_t N>
void MyMethod(T (&myArray)[N])
{
//N is number of elements, myArray is the array
std::cout<<"array elements number = "<<N<<endl;
//put your code
string temp;
temp.resize(N+1);//this is for performance not to copy it each time you use += operator
int i = 0;
while (i < max)
{
temp += store[i];
i++;
}
cout << temp << endl;
}
//call it like this
char arr[] = "hello world";
MyMethod(arr);
This is what I have to do:
A teacher has asked all her students to line up single file according to their first name. For example, in one class Amy will be at the front of the line and Yolanda will be at the end. Write a program that prompts the user to enter the number of students in the class, then loops to read in that many names. Once all the names have been read in it reports which student wourld be at the front of the line and which one would be at the end of the line. You may assume that no two students have the same name. Input Validation: Do not accept a number less than 1 or greater than 25 for the number of students.
This is what I have so far:
#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
int main()
{
int StudentNum;
cout << "How many student are in the class?\n";
cin >> StudentNum;
char sname[StudentNum + 1][25];
if (StudentNum < 1 || StudentNum > 25)
{
cout << "Please enter a number between 1-25 and try again\n";
return 0;
}
for (int i = 1; i <= StudentNum; i++);
{
cout << "Please enter the name of student #" << i << endl;
cin >> sname[i];
}
for (int output = 0; output <=StudentNum; output++);
{
cout << endl << sname[output] << endl;
}
system ("pause");
return 0;
}
Am I missing something about arrays??
You cannot create such an array because its length has to be known at compile time (i.e., it cannot be the result of an expression such as StudentNum + 1).
You can solve this issue because by the problem definition you know an upper bound for the array size, so you can use that as a compile time constant.
However, this problem can be solved without using an array at all. Read the wording carefully.
Hint for the solution without arrays: Think of the array as a single piece of paper (variable) with all the names written one after another. Not using an array then means that you have to be able to solve the problem without looking at all the names at once. How would you come to the answer if I only allowed you to see the names one by one?
Another hint: The problem is still solvable if there were several trillion students in the class (with unique names no less), i.e. more than could possibly fit in the computer's memory at any one time.
C++ array dimensions must be known at compile time (ie not dependent on user-entered variables at run-time). Use strings instead:
string sname[25];
If you were using something besides char arrays, you could also use a vector.
Think about what the problem statement is actually asking for. Your program only needs to output the first and last names alphabetically. Do you actually need to store all the names to do that?
Just for fun, here's how I would do it. Don't turn this in unless are ready to explain to your teacher how it works.
struct MinMax {
std::string min;
std::string max;
MinMax& operator+(const std::string& kid) {
if( min.empty() || kid < min) min = kid;
if( max.empty() || kid > max) max = kid;
return *this;
}
};
int main() {
int nKids;
std::cout << "How many students? " << std::flush;
std::cin >> nKids;
std::cout << "Enter students' names, followed by EOF\n";
MinMax mm(std::accumulate(
std::istream_iterator<std::string>(std::cin),
std::istream_iterator<std::string>(),
MinMax()));
std::cout << mm.min << ", " << mm.max << "\n";
}
What i'm trying to do is create a template array class that will store values of a data type into an array. I have it working fine with int values, however working with string objects things start to break down.
I've taken out the block of code and tried it on it's own and I do get the same error. I'm sure I've learnt this, and I'm almost positive that the answer is something simple, trying to wrap my head around the pace in which we're learning c++ is a little crazy at times!
My best guess right now, is that I would need to tokenize the string and look for spaces. I tend to over think things though which lead to more confusion - thus me seeking out a answer here!
The code:
// Test String: Hello World this is a String Object
int stringSize = 7;
int count = 0;
string s[stringSize];
cout << "\nEnter " << stringSize << " one-word string values:\n";
while (count < stringSize) {
string tmpVal;
cin >> tmpVal;
s[count] = tmpVal;
count ++;
}
string s[stringSize]; is illegal because stringSize is not a constant. You must either use dynamic memory (i.e. string* s = new string [stringSize];), include stringsize as a template argument (don't do this, it doesn't actually solve the problem), use a fixed size value, or use an existing structure (I'd suggest vector, as in Bill's answer). The code below works fine on my compiler:
int main(int argc, char *argv[]) {
int stringSize = 7;
int count = 0;
string* s = new string [stringSize];
cout << "\nEnter " << stringSize << " one-word string values:\n";
while (count < stringSize) {
string tmpVal;
cin >> tmpVal;
s[count] = tmpVal;
count ++;
}
delete[] s;
}
I am a little confused as to exactly what you're looking for, but I suggest looking into the standard library.
Perhaps something like:
list<string> s;
and then, in the loop use push_back.
I am also confused what is your actual question, because your code works. However, FWIW, I would suggest the following. The changes are: (1) use of const (already suggested by others), (2) use of size_t, (3) change of variable name stringSize to numStrings (because of this I was confused at first glance), and (4) avoiding string copy.
#include <iostream>
#include <string>
using namespace std;
int main()
{
const size_t numStrings = 7;
size_t count = 0;
string s[ numStrings ];
cout << "\nEnter " << numStrings << " one-word string values:\n";
while (count < numStrings) {
cin >> s[ count ];
count++;
}
return 0;
}
Why not read in the entire line, then find all spaces and using the substr method, split the string?
You will need the following methods:
getline()
find_first_of()
substr()
Also, searching around this site for splitting strings in c++ will give you a lot of tips.
First of all, the size of your array should be constant:
const int stringSize = 7;
Secondly, as dbrien said, you should use std::vector unless you're doing this for the learning experience:
std::string tmpVal;
std::vector<std::string> s;
cout << "\nEnter " << stringSize << " one-word string values:\n";
while (cin >> tmpVal)
{
s.push_back(tmpVal);
}
First, the array dimension must be constant, so it should be const int stringsize = 7; Also, I would suggest using std::vector rather than std::list, additionally What was the error?
Not sure what error you're getting, but this is wrong because you need to use a constant integral value to allocate arrays on the stack.. Change:
int stringSize = 7;
int count = 0;
string s[stringSize];
... to:
const int stringSize = 7;
int count = 0;
string s[stringSize];
You can and probably should also use a vector instead of using C-style arrays, or trying to hand roll your own templated array class:
vector<string> s;
const int stringSize = 7;
cout << "\nEnter " << stringSize << " one-word string values:\n";
while (s.size() < stringSize) {
string tmpVal;
cin >> tmpVal;
s.push_back(tmpVal);
}
So it turns out it was the compiler. I was using xCode and getting:
cin_cout(7307) malloc: *** error for object 0x1000072c0: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
Running the same block in Visual c++ seemed to be ok... Sorry for my stupidity and thanks kindly for all the quick feedback!