I'm working on an assignment where we have to create a "MyInt" class that can handle larger numbers than regular ints. We only have to handle non-negative numbers. I need to overload the >> operator for this class, but I'm struggling to do that.
I'm not allowed to #include <string>.
Is there a way to:
a. Accept input as a C-style string
b. Parse through it and check for white space and non-numbers (i.e. if the prompt is cin >> x >> y >> ch, and the user enters 1000 934H, to accept that input as two MyInts and then a char).
I'm assuming it has something to do with peek() and get(), but I'm having trouble figuring out where they come in.
I'd rather not know exactly how to do it! Just point me in the right direction.
Here's my constructor, so you can get an idea for what the class is (I also have a conversion constructor for const char *.
MyInt::MyInt (int n)
{
maxsize = 1;
for (int i = n; i > 9; i /= 10) {
// Divides the number by 10 to find the number of times it is divisible; that is the length
maxsize++;
}
intstring = new int[maxsize];
for (int j = (maxsize - 1); j >= 0; j--) {
// Copies the integer into an integer array by use of the modulus operator
intstring[j] = n % 10;
n = n / 10;
}
}
Thanks! Sorry if this question is vague, I'm still new to this. Let me know if I can provide any more info to make the question clearer.
So what you basically want is to parse a const char* to retrieve a integer number inside it, and ignore all whitespace(+others?) characters.
Remember that characters like '1' or 'M' or even ' ' are just integers, mapped to the ASCII table. So you can easily convert a character from its notation human-readable ('a') to its value in memory. There are plenty of sources on ascii table and chars in C/C++ so i'll let you find it, but you should get the idea. In C/C++, characters are numbers (of type char).
With this, you then know you can perform operations on them, like addition, or comparison.
Last thing when dealing with C-strings : they are null-terminated, meaning that the character '\0' is placed right after their last used character.
Related
I'm currently trying to design an algorithm that doing such thing:
I got two strings A and B which consist of lowercase characters 'a'-'z'
and I can modify string A using the following operations:
1. Select two characters 'c1' and 'c2' from the character set ['a'-'z'].
2. Replace all characters 'c1' in string A with character 'c2'.
I need to find the minimum number of operations needed to convert string A to string B when possible.
I have 2 ideas that didn't work
1. Simple range-based for cycle that changes string B and compares it with A.
2. Idea with map<char, int> that does the same.
Right now I'm stuck on unit-testing with such situation : 'ab' is transferable to 'ba' in 3 iterations and 'abc' to 'bca' in 4 iterations.
My algorithm is wrong and I need some fresh ideas or working solution.
Can anyone help with this?
Here is some code that shows minimal RepEx:
int Transform(string& A, string& B)
{
int count = 0;
if(A.size() != B.size()){
return -1;
}
for(int i = A.size() - 1; i >= 0; i--){
if(A[i]!=B[i]){
char rep_elem = A[i];
++count;
replace(A.begin(),A.end(),rep_elem,B[i]);
}
}
if(A != B){
return -1;
}
return count;
}
How can I improve this or I should find another ideas?
First of all, don't worry about string operations. Your problem is algorithmic, not textual. You should somehow analyze your data, and only afterwards print your solution.
Start with building a data structure which tells, for each letter, which letter it should be replaced with. Use an array (or std::map<char, char> — it should conceptually be similar, but have different syntax).
If you discover that you should convert a letter to two different letters — error, conversion impossible. Otherwise, count the number of non-trivial cycles in the conversion graph.
The length of your solution will be the number of letters which shouldn't be replaced by themselves plus the number of cycles.
I think the code to implement this would be too long to be helpful.
This question already has answers here:
How to strip all non alphanumeric characters from a string in c++?
(12 answers)
Closed 6 years ago.
I'm trying to remove all non alphabet characters from an inputed string in c++ and don't know how to. I know it probably involves ascii numbers because that's what we're learning about. I can't figure out how to remove them. We only learned up to loops and haven't started arrays yet. Not sure what to do.
If the string is Hello 1234 World&*
It would print HelloWorld
If you use std::string and STL, you can:
string s("Hello 1234 World&*");
s.erase(remove_if(s.begin(), s.end(), [](char c) { return !isalpha(c); } ), s.end());
http://ideone.com/OIsJmb
Note: If you want to be able to handle strings holding text in just about any language except English, or where programs use a locale other than the default, you can use isalpha(std::locale).
PS: If you use a c-style string such as char *, you can convert it to std::string by its constructor, and convert back by its member function c_str().
If you're working with C-style strings (e.g. char* str = "foobar") then you can't "remove" characters from a string trivially (as a string is just a sequence of characters stored sequentially in memory - removing a character means copying bytes forward to fill the empty space used by the deleted character.
You'd have to allocate space for a new string and copy characters into it as-needed. The problem is, you have to allocate memory before you fill it, so you'd over-allocate memory unless you do an initial pass to get a count of the number of characters remaining in the string.
Like so:
void BlatentlyObviousHomeworkExercise() {
char* str = "someString";
size_t strLength = ... // how `strLength` is set depends on how `str` gets its value, if it's a literal then using the `sizeof` operator is fine, otherwise use `strlen` (assuming it's a null-terminated string).
size_t finalLength = 0;
for(size_t i = 0; i < strLength; i++ ) {
char c = str[i]; // get the ith element of the `str` array.
if( IsAlphabetical(c) ) finalLength++;
}
char* filteredString = new char[ finalLength + 1 ]; // note I use `new[]` instead of `malloc` as this is C++, not C. Use the right idioms :) The +1 is for the null-terminator.
size_t filteredStringI = 0;
for(size_t i = 0; i < strLength; i++ ) {
char c = str[i];
if( IsAlphabetical(c) ) filteredString[ filteredStringI++ ] = c;
}
filteredString[ filteredStringI ] = '\0'; // set the null terminator
}
bool IsAlphabet(char c) { // `IsAlphabet` rather than `IsNonAlphabet` to avoid negatives in function names/behaviors for simplicity
return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
}
I do not want to spoil the solution so I will not type out the code, only describe the solution. For your problem think of iterating through your string. Start with that. Then you need to decide if the currently selected character is part of the alphabet or not. You can do this numerous different ways. Checking ASCII values? Comparing against a string of the alphabet? Once you decide if it is a letter, then you need to rebuild the new string with that letter plus the valid letters before and after that you found or will find. Finally you need to display your new string.
If you look at an ascii table, you can see that A-Z is between 65-90 and a-z is between 97-122.
So, assuming that you only need to remove those characters (not accentuated), and not other characters from other languages for example, not represented in ascii, all you would need to do is loop the string, verify if each char is in these values and remove it.
I have a program set up already to read in a file and split each line into words, storing them into a double vector of strings. That is,
std::vector < std::vector <std::string> > words
So, the idea is to use an array from alphabet a-z and using the ASCII values of the letters to get the index and swapping the characters in the strings with the appropriate shifted character. How would I get the value of each character so that I can look it up as an index?
I also want to keep numbers intact, as a shift cipher, I believe, doesn't do anything with numbers in the text to be deciphered. How would I check if the character is an int so I can leave it alone?
If you want the ASCII value, you simply have to cast the value to a int:
int ascii_value = (int)words[i][j][k];
If you want to have a value starting from A or a you can do this:
int letter_value_from_A = (int)(words[i][j][k] - 'A');
int letter_value_from_a = (int)(words[i][j][k] - 'a');
Your char is nothing else than a value. Take this code as example (I am used to program C++11, so this will be a little ugly):
char shiftarray[256] = {0, 0, 0, 0 // Here comes your map //
std::string output;
for(int w=0; w<words.length(); w++)
{
for(int c=0; c<words[w].length(); c++)
{
output.pushback(shiftarry[words[w][c]]);
}
output.push_back(' ');
}
I do not know how to do it in anything other than basic, but very simply get the ascii value of each letter in the string using a loop. As the loop continues add a value to, or subtract a value from the ascii value you just obtained, then convert it back to a letter and append it to a string. This will give you a different character than you had originally. By doing this, you can load and save data that will look like gibberish if anyone tried to view it other than in the program it was written in. The data then becomes a special propriatry document format.
How can I convert the char in the array into an integer?
Ignore lines 5-100 it is just my stack.
http://ideone.com/KQytD
Scroll down output #2 worked properly but output #3 did not. Some how when I pushed the value back into the stack and when I popped it it had the +'43' because of the ASCII and I cannot seem to get it into a regular integer value so I can do these operations easily.
line 116 puts input into char postfix. NOTE: input must be in postfix notation line 117 puts the single integer value into final after it has run through the function.
convertPostfixToEvaluation works as such: I scroll through each index of postfix until I read in '=' then I output the total/sum. The first if statement pushed the operands (0-9) into a stack. The second if statement if it reads in an operator then it attempts to do the operation as such in lines 134-158. After the if statements I increase the index value by 1 so it can scan the entire array.
The issue lies within the switch where I try adding,subtracting,multiply, or dividing more than 3 operands. so the 3rd one i believe is still has the value (+43 because of the ASCII).
My outputs(on the bottom of my program) show what the awkwardness is.
The cut to the chase issue. Issue converting char to int the second time around.
There are many things very likely wrong with this code.
Look up the function isdigit. This should eliminate the huge if statement.
You may want to use a string lookup instead of the other complex if statement:
const std::string my_operators = "+-/*";
if (my_operators.find(postfix[i]) != std::string::npos)
{
// Enter here if the character is a valid symbol.
}
If you "parse" character by character, you will have to build your number:
int number = 0;
// After detecting the character is a number:
number = number * 10 + (postfix[i] - '0');
The expression "postfix[i] - '0'" will return the distance between the number character and the character for zero. The C and C++ languages guarantee the following relationship:
'0' < '1' < '2' < '3' < '4' < '5' < '6' < '7' < '8' < '9'
The languages also state that those numbers are contiguous.
Suggestion: use std::string instead of an array of characters. The std::string contains some helpful functions for searching, skipping characters, and obtaining a substring.
Currently I'm working on an assignment and using C++ for the first time.
I'm trying to append certain "message types" to the beginning of strings so when sent to the server/client it will deal with the strings depending on the message type. I was wondering if I would be able to put any two-digit integer into an element of the message buffer.... see below.
I've left a section of the code below:
char messageBuffer[32];
messageBuffer[0] = '10'; << I get an overflow here
messageBuffer[1] = '0';
for (int i = 2; i < (userName.size() + 2); i++)
{
messageBuffer[i] = userName[(i - 2)];
}
Thanks =)
'10' is not a valid value, thus the overflow
either write 10 as in messageBuffer[0]=10 - if ten is the value you want to put it or do as Lars wrote.
The message buffer is an array of char. Index 0 contains one char, so you cannot put 2 chars into one char. That would violate the rule that one bit contains one binary digit :-)
The correct solution is to do this:
messageBuffer[0]='0';
messageBuffer[1]='1';
or:
messageBuffer[1]='0';
messageBuffer[0]='1';
or
messageBuffer[0]=10;