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I wrote a program which is supposed to remove excess spaces from a string. But it only shows characters before spaces. It finds a space and checks the character after that whether it is a space. Depending on excess spaces it shifts other characters over excess spaces. But output is very confusing.

input: "qwe(2 spaces)rt(one space)y"

output: "qwe(one space)rt(one space)y"

#include <iostream>
#include <stdlib.h>
#include <string>

using namespace std;

int main(){
    string a;
    cin >> a;
    int len = a.length();
    int new_len=len;
    int z,s=0;
    for(int i=0; i<new_len; i++){
        if(a[i]==' '){
            z=i+1;
            s=0;
            //Assigning the number of excess spaces to s.
            while(a[z]==' '){
                s++;
                z++;
            }
            //doing the shifting here.
            if(s>0){
                for(int l=i+1; l<new_len-s; l++){
                    a[l]=a[s+l];
                }
            }
            new_len-=s;
        }

    }
    cout << a << endl;
    cout << a.length();
    system("pause");
    return 0;
}
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  • Did you debug your code? Commented Mar 15, 2013 at 5:26
  • 2
    Is this what you're trying to do? stackoverflow.com/questions/8362094/… Commented Mar 15, 2013 at 5:26
  • I would consult std::string and consider doing it a little more efficiently using find_first_of() and find_first_not_of() and their simulars. Commented Mar 15, 2013 at 5:28
  • std::string a; cin >> a; skips leading whitespace and only reads data into a until it hits more whitespace (which isn't read into a) or end-of-file, so you can't possibly have input with any whitespace to strip. If you'd put cout << "a '" << a << "'\n"; into your program you'd have noticed: such "trace" output is an essential diagnostic for programming, and would let you watch your program work.... Commented Mar 15, 2013 at 5:32

3 Answers 3

Reset to default
1

Most of your code is semi-pointless -- when you use the normal string extractor (stream >> string) it automatically skips across all consecutive leading white-space, and stops reading at the first whitespace character. As such, it's already doing almost everything the rest of your code is intended to accomplish. That leaves a much simpler approach to accomplishing the same task:

std::copy(std::istream_iterator<std::string>(std::cin),
          std::istream_iterator<std::string>(),
          std::ostream_iterator<std::string>(std::cout, " "));

This does have one problem: it'll leave one extra space at the end of the output. If you don't want that, you can use the infix_ostream_iterator I've posted previously. With that, you'd change the above to something like this:

std::copy(std::istream_iterator<std::string>(std::cin),
          std::istream_iterator<std::string>(),
          infix_ostream_iterator<std::string>(std::cout, " "));
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1 Comment

I don't understand this code. But it might be the solution.
1

If you're using C++11 doing this your way is overkill - you can just use a regex. Something like the following should do it (untested):

#include <regex>
#include <iostream>
#include <string>
using namespace::std;

int main(){
  string a;
  cin >> a;
  regex r(" +");
  a = regex_replace(a,r," ");
  cout << a << endl;
  cout << a.length();
  system("pause");
  return 0;
}
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1

Your code is highly ineffective. Imagine a following string with 1,000,000 characters:

a  a  a  a  a  a  a...

Each time your algorithm encounters a second space, it goes through the whole string to shift it one char left. I would attempt another approach:

  • Create two iterators, like realPos and charPos. Set them to 0 at the beginning.
  • Create a variable, which stores a number of spaces encountered so far, like spacesSeen. Set it to 0.
  • Now, while realPos is lower than length of the whole string:
    • If string[realPos] != ' ' and charPos != realPos, make an assignment: string[charPos] = string[realPos]. Then increase both realPos and charPos by one. Set spacesSeen to 0.
    • If string[realPos] == ' ' and spacesSeen == 0, increase spacesSeen by one, copy characters and advance both iterators.
    • If string[realPos] == ' ' and spacesSeen > 0, then increase spacesSeen and then increase only realPos.
  • Now charPos marks the place where your final string ends, adjust strings size, such that it ends there.

In simpler words: copy the characters one by one and skip multiple spaces on the way.

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