CODEWITHSUNDEEP
c++string
Sarp Kaya
Sarp Kaya

Reputation: 3784

How to change a char in a string in C++

I was trying to solve this problem but I think I am not doing the string handling part right. The problem is given a string (let's say "abc") write out all upper and lower case combinations of this string.

My approach was to modify binary counter method.

So here's my implementation:

#include <iostream>
#include <cmath>

#define LOWER_CASE_DIFF 'a'-'A'

using namespace std;

void changeSeq(string &in, int amount) {
    int i = 0;
    while (i < amount && (int)in[i] < 'a') {
        in[i] += LOWER_CASE_DIFF;
        i++;
    }
    if (i < amount) {
        in[i] -= LOWER_CASE_DIFF;
    }
    cout << in << endl;
}
int main() {
    string input = "abc";
    int diff = 'a' - 'A'; //a is always bigger than A in ASCII
    int comb = (int)pow(2,(float)input.length());
    for (int i = 1; i <= comb; i++) {
        changeSeq(input, i);    
    }


    return 0;
}

I am getting this runtime error:

/usr/local/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../../include/c++/4.1.2/bits/basic_string.h:707: typename _Alloc::rebind<_CharT>::other::reference std::basic_string<_CharT, _Traits, _Alloc>::operator[](typename _Alloc::rebind<_CharT>::other::size_type) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]: Assertion '__pos < size()' failed.

Disallowed system call: SYS_kill

So how can I change one character at a time? Is strings behaviour in C++ similar to const char* str = "abc" in C, where array of characters are stored in constants?

Upvotes: 0

Views: 1009

Answers (3)

Pandrei
Pandrei

Reputation: 4951

I think you are over-complicating thing when trying to compute the number of possible outputs; maybe this'll help:

for(i=0;i<input.length();i++)
{
 for(j=0;j<input.length();j++)
 {
  printString(input);
  changeCase(input[j]);
 }
 printString(input);
 changeCase(input[i]);
}

Upvotes: 0

AndersK
AndersK

Reputation: 36082

You could do something like this

  string s = "ABC";
  int comb = 1 << s.length();
  for (int i = 0; i < comb; ++i) // 0000 0001 0010 ... 1000
  {
    for ( size_t j = 0; j < s.length(); ++j )
    {
      if ( i & (1 << j) )
      { 
        s[j] = tolower(s[j]); 
      }
      else
      { 
        s[j] = toupper(s[j]); 
      }
    }
    cout << s << endl;
  }

probably would be better to include a 

bool testbit(int value, int bit)
{
  return value & (1 << bit);
}

to make the code more readable.

Upvotes: 1

Caesar
Caesar

Reputation: 9843

You need to include the string header

#include <string>

Other then that, it seems to be working fine in VS2013

Upvotes: 0

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