Imprecision when passing from string to int character by character in c++ - c++

First of all I am taking the string from geline(cin, s) and the input is in the form of: 100 49. And I can not take it with normal cin because I need to know where geline(cin, s) makes s empty so that means is a blank line and I should stop the program.
When passing from string '99' (or any other number below 100) to int 99 there is no problem. But when I try a number greater than 99 it gave the (number - 1). Also I found that this happens with numbers below 1000 but from 1000 to 10000 it is ok, but I tested number greater than 10^4 and it gave the (number - 1) another time.
Here is my code to convert the string
//Search how many nums are in the string wer are passing until an space or new line
int nums = 0;
for(int j = i; j < s.size(); j++){
if(s[j] == ' ' || s[j] == '\n') break;
nums++;
}
//pass to the variable time the string character by character
int time = 0;
while(nums--){
time += (s[i] - '0') * (pow(10, nums));
i++;
}
I would like to know if there is an error from my computer or I am missing something.

First of all I am taking the string from geline(cin, s) and the input is in the form of: 100 49.
Then simplest solution is to use std::istringstream:
int i1 = 0, i2 = 0;
std::istringstream( s ) >> i1 >> i2;

Related

unexpected value in my code and how I fix it

My assignment:
The teacher has written down the sum of multiple numbers. Pupils should calculate the sum. To make the calculation easier, the sum only contains numbers 1, 2 and 3. Still, that isn't enough for Xenia. She is only beginning to count, so she can calculate a sum only if the summands follow in non-decreasing order. For example, she can't calculate sum 1+3+2+1 but she can calculate sums 1+1+2 and 3+3.
You've got the sum that was written on the board. Rearrange the summons and print the sum in such a way that Xenia can calculate the sum.
Input
The first line contains a non-empty string s — the sum Xenia needs to count. String s contains no spaces. It only contains digits and characters "+". Besides, string s is a correct sum of numbers 1, 2, and 3. String s is at most 100 characters long.
Output
Print the new sum that Xenia can count.
Examples:
Input
3+2+1
Output
1+2+3
Here is my solution:
#include<string>
#include <iostream>
using namespace std;
int main()
{
string su ;
cin >> su;
int n, temp ;
n = su.size();
for (int i = 0 ; i < n ; i+=2)
{
if (su[i]=='1')
{
su[i]-='0';
}
else if (su[i]=='2')
{
su[i]-='0';
}
else if ( su[i]== '3')
{
su[i]-='0';
}
}
for (int i =0 ; i <n ; i+=2)
{
for(int j = 0 ; j< n; j+=2 )
{
if (su[i]< su [j])
{
temp = su[i];
su[i]=su[j];
su[j]=temp;
}
}
}
for(int i = 0 ; i < n ; i++)
{
if(su[i]=='+')
{
cout<<su[i];
}
else
cout<<su[i];//this is the line I can't understand why the result like that;
}
}
the problem is when I run the code with input 3+2+1 i expect the output is 1+2+3+ but I get ?+?+? something like that and I can't understand the reason.
First doing the s[i] -= '0' is very dangerous as it is a string, you should do int myNum = s[i] - '0' instead and then try storing it inside of the string, because when you do s[i] -= '0' it is never casted into an integer, but it stays char all the time so if you do not cast it to integer, it will go ascii code of '1' - '0' okay that is 1, which symbol has an ascii code of one? Oh it's the SOH character... And it takes the SOH character and put it inside of your string, but you string does not know what SOH is so it goes ???..(just joking, strings do not have emotions). All jokes aside the strange behavior is probably caused by you trying to store an illegal character inside a string. I would convert the '1' - '0' to int first.... Then store it in a string.

Why calculate the remainders here?

I am trying to solve a question on LeetCode.com:
An encoded string S is given. To find and write the decoded string to a tape, the encoded string is read one character at a time and the following steps are taken:
If the character read is a letter, that letter is written onto the tape.
If the character read is a digit (say d), the entire current tape is repeatedly written d-1 more times in total.
Now for some encoded string S, and an index K, find and return the K-th letter (1 indexed) in the decoded string.
The most upvoted solution goes like this:
string decodeAtIndex(string S, int K) {
long N = 0, i;
for (i = 0; N < K; ++i)
N = isdigit(S[i]) ? N * (S[i] - '0') : N + 1;
while (i--)
if (isdigit(S[i]))
N /= S[i] - '0', K %= N; // what's the intuition for this
else if (K % N-- == 0) // and this?
return string(1, S[i]);
return "lee215";
}
While I carried out a dry-run over the code using pen-and-paper, I am not sure I fully understand the intuition behind the commented lines.
How does this work?

How does strings comparison in C++ work?

I am trying to solve this problem.
I am implementing it with strings. Here is my code snippet
string s,ss;
// s and ss both contains integer input.
while(s <= ss )
//while( s<=ss && s.size() <= ss.size())
{
int i = inc, j = dec; // inc and dec are middle values. both equal if odd else different
while((s[j]-'0')==9 && i < len && j>=0){
// for cases like 999
s[i] = s[j] = '0';
i++;
j--;
}
if(j<0){
s = "1" + s;
int l = s[len-1] - '0';
l++;
//cout<<l<<"\n";
s[len] = (l + '0');
}
else{
int l = s[j] - '0';
l++;
s[i] = s[j] = (l+'0');
}
if(s <= ss)
cout<<"out in wild "<<s<<" and "<<ss<<"\n";
}
cout<<s<<endl;
The problem that I am facing is when input is like 999 or 9999. The outer while loop keeps on looping even when the value of s increases, but if I add while( s<=ss && s.size() <= ss.size()) it works completely fine. Why is while(s<=ss) is not working? I rarely use the string class, so I don't understand it completely. Why don't string s= 101 and ss=99 stop the while loop?
Complete code link is here
You are comparing strings with lexicographical order, not numbers , so "101" is less than "99" (because '1' < '9') , e.g.
int main(){
std::string s = "99";
std::string ss = "101";
std::cout << std::boolalpha << (s <= ss);
}
Outputs false.
Notes:
A better design for your program would be to manipulate numbers (int or double ...) and not strings in the first place, so this kind of expressions would naturally work as you expect.
E.g. "101" + "99" is "10199", not "200" ...
But if you really need strings, consider this post to sort strings containing numbers.
As pointed by #Deduplicator, a program that needlessly overuses strings is sometimes called Stringly Typed
Also see std::lexicographical_compare
Since your input explicitly only involves positive integers without leading 0, writing a comparison function is trivial, something like : (untested)
/* Returns 1 if the integer represented by s1 > the integer represented by s2
* Returns -1 if the integer represented by s1 < the integer represented by s2
* Return 0 is both are equals
*
* s1 and s2 must be strings representing positive integers without trailing 0
*/
int compare(const std::string& s1, const std::string& s2)
{
if(s1.size() > s2.size())
return 1;
if(s2.size() > s1.size())
return -1;
for(std::size_t i = 0 ; i < s1.size() ; ++i)
{
if(s1[i] - '0' < s2[i] - '0')
return 1;
if(s2[i] - '0' < s1[i] - '0')
return -1;
}
return 0;
}
While s and ss are string variables, they are compared character by character.
In the case that you mentioned being: s = "101" & ss = "99", by first hand it will check the first character in each string, and as '1' < '9' it exit up with s < ss. I would advise you to convert those values to integers before comparison.
As the s is compared with ss in lexicographical order, I would suggest you to compare one char from tail with one char from head (one by one till you reach the middle) to solve that problem.

How to replace certain items in a char array with an integer in C++?

Below is an example code that is not working the way I want.
#include <iostream>
using namespace std;
int main()
{
char testArray[] = "1 test";
int numReplace = 2;
testArray[0] = (int)numReplace;
cout<< testArray<<endl; //output is "? test" I wanted it 2, not a '?' there
//I was trying different things and hoping (int) helped
testArray[0] = '2';
cout<<testArray<<endl;//"2 test" which is what I want, but it was hardcoded in
//Is there a way to do it based on a variable?
return 0;
}
In a string with characters and integers, how do you go about replacing numbers? And when implementing this, is it different between doing it in C and C++?
If numReplace will be in range [0,9] you can do :-
testArray[0] = numReplace + '0';
If numReplace is outside [0,9] you need to
a) convert numReplace into string equivalent
b) code a function to replace a part of string by another evaluated in (a)
Ref: Best way to replace a part of string by another in c and other relevant post on SO
Also, since this is C++ code, you might consider using std::string, here replacement, number to string conversion, etc are much simpler.
You should look over the ASCII table over here: http://www.asciitable.com/
It's very comfortable - always look on the Decimal column for the ASCII value you're using.
In the line: TestArray[0] = (int)numreplace; You've actually put in the first spot the character with the decimal ASCII value of 2. numReplace + '0' could do the trick :)
About the C/C++ question, it is the same in both and about the characters and integers...
You should look for your number start and ending.
You should make a loop that'll look like this:
int temp = 0, numberLen, i, j, isOk = 1, isOk2 = 1, from, to, num;
char str[] = "asd 12983 asd";//will be added 1 to.
char *nstr;
for(i = 0 ; i < strlen(str) && isOk ; i++)
{
if(str[i] >= '0' && str[i] <= '9')
{
from = i;
for(j = i ; j < strlen(str) && isOk2)
{
if(str[j] < '0' || str[j] > '9')//not a number;
{
to=j-1;
isOk2 = 0;
}
}
isOk = 0; //for the loop to stop.
}
}
numberLen = to-from+1;
nstr = malloc(sizeof(char)*numberLen);//creating a string with the length of the number.
for(i = from ; i <= to ; i++)
{
nstr[i-from] = str[i];
}
/*nstr now contains the number*/
num = atoi(numstr);
num++; //adding - we wanted to have the number+1 in string.
itoa(num, nstr, 10);//putting num into nstr
for(i = from ; i <= to ; i++)
{
str[i] = nstr[i-from];
}
/*Now the string will contain "asd 12984 asd"*/
By the way, the most efficient way would probably be just looking for the last digit and add 1 to it's value (ASCII again) as the numbers in ASCII are following each other - '0'=48, '1'=49 and so on. But I just showed you how to treat them as numbers and work with them as integers and so. Hope it helped :)

Arithmetic on C++ strings

This code really confuses me, it is using some Stanford libraries for the Vector (array) class. Can anyone tell me what is the purpose of int index = line [j] - 'a'; why - 'a'?
void countLetters(string filename)
{
Vector<int> result;
ifstream in2;
in2.open(filename.c_str());
if (in.fail()) Error("Couldn't read '" + filename + "'");
for (int i = 0; i < ALPHABETH_SIZE; i++)
{
result.add(0); // Must initialize contents of array
}
string line;
while (true)
{
getLine(in, line);
// Check that we got a line
if (in.fail()) break;
line = ConvertToLowerCase(line);
for (int j = 0; j < line.length(); j++)
{
int index = line [j] - 'a';
if (index >= 0 && index < ALPHABETH_SIZE)
{
int prevTotal = result[index];
result[index] = prevTotal +1;
}
}
}
}
The purpose of the code:
Takes a filename and prints the number of times each letter of the alphabet appears in that file. Because there are 26 numbers to be printed, CountLetters needs to create a Vector. For example, if the file is:
Characters in a string are encoded using a character set... typically ASCII on hardware common in English language systems. You can see the ASCII table at http://en.wikipedia.org/wiki/ASCII
In ASCII (and most other character sets), the numbers representing letters are contiguous. So, this is the natural way to test whether the character at index j in character-array line is a letter:
line[j] >= 'a' && line[j] <= 'z'
Your program is equivalent to that, in an algebra-kind of sense it subtracts a from both sides (knowing that a is the first character in the character set):
line[j] >= 'a' - `a` && line[j] <= 'z' - `a`
line[j] >= 0 && line[j] <= 'z' - `a`
Replacing "<= z - a" with am equivalent:
line[j] >= 0 && line[j] < ALPHABET_SIZE
where ALPHABET_SIZE is 26. This trades a dependency on knowing z is the last character of your character set for knowing how many characters are in your character set - both are a little fragile, but fine if you know you're dealing with a well-known, stable character set encoding.
A better way to check for a letter is to use the isalpha() predicate: http://www.cplusplus.com/reference/clibrary/cctype/isalpha/
"a" is at the beginning of ASII chars.
int index = line [j] - 'a';
if (index >= 0 && index < ALPHABETH_SIZE)
These two line of code is to just if line[j] is a character.