How to convert a sentence from upper case to lower case that contains space and numbers

Question

I'm trying to convert a sentence from upper case to lowercase. I also write a code but I stopper when a space is appear. How can I fix this problem and convert the whole sentence? Here is my code

#include<iostream>
#include<cstring>
using namespace std;
int main()
{
    char str[100];
    cin>>str;
    for(int i=0;i<strlen(str);i++)
    {
        if(str[i]>='A'&&str[i]<='Z')
        {
            str[i]=str[i]+32;
        }
    }
    cout<<str<<endl;
    return 0;
}

Use `std::transform` or the already made Boost algorithms. And use `std::string`; you're asking for a buffer overrun. — chris, Nov 09 '13 at 15:43
OP, I hope this experience hasn't soured you on white space because your code could use a little more of it for readability purposes. — Duck, Nov 09 '13 at 15:46
This code assumes that the characters `A`-`Z` have contiguous values, the characters `a`-`z` have contiguous values, and that a character can be converted to lowercase by adding 32. While that's true for ASCII, it's not true for every character set. Read about `to lower` in the standard library. — Pete Becker, Nov 09 '13 at 15:58

score 1 · Answer 1 · answered Nov 09 '13 at 15:43

It's because of theinput operator >>, it breaks on space. If you want to read a whole line then use std::getline to read into a std::string instead.

Then read about the C++ standard algorithms, like for example std::transform. Also, std::tolower doesn't modify anything that's not an upper-case letter, so it's a good function to use.

score 0 · Answer 2 · answered Nov 09 '13 at 15:48

The error is because operator>> delimites on spaces. The alternative is to use getline. See the following example:

#include <cstring>
#include <iostream>
#include <string>

int main() {
  std::string s;

  std::getline(std::cin, s);

  std::cout << "Original string: " << s << std::endl;

  if (!std::cin.fail()) {
    const int len = strlen(s.c_str());

    for (size_t i = 0; len > i; ++i) {
      if ((s[i] >= 'A') && (s[i] <= 'Z'))
        s[i] = s[i] - 'A' + 'a';
    }
  }

  std::cout << "New string: " << s << std::endl;

  return 0;
}

score 0 · Answer 3 · answered Nov 09 '13 at 16:05

The reason input stops at whitespace is because formatted input is delimited by whitespace characters (among others). You will need unformatted I/O in order to extract the entire string into str. One way to do this is to use std::istream::getline:

std::cin.getline(str, 100, '\n');

It's also useful to check if the input succeeded by using gcount:

if (std::cin.getline(str, 100, '\n') && std::cin.gcount())
{
    ...
}

But in practice it's recommended that you use the standard string object std::string which holds a dynamic buffer. To extract the entire input you use std::getline:

std::string str;

if (std::getline(std::cin, str)
{
    ...
}

score 0 · Answer 4 · answered Nov 30 '16 at 14:19

Here is one of the examples of doing it using transform function.

#include <iostream>
#include <string>
#include <algorithm>

using namespace std;

int main()
{
    string str;

    if (getline(cin, str))
    {
        transform(str.begin(), str.end(), str.begin(), ptr_fun<int, int>(toupper));
    }

    cout << str << endl;
    return 0;
}

How to convert a sentence from upper case to lower case that contains space and numbers

4 Answers4