Transformation to lower case in C++ - c++

Question

#include<iostream>
#include<string>
#include<cstring>
#include<cstdio>
#include<cstdlib>
#include <string>
#include <algorithm>
using namespace std;
string A,B;
int main()
{
int t,l,i;
scanf("%d",&t);
while(t--)
{
std::string str;
std::getline(cin, str);
std::transform(str.begin(), str.end(), str.begin(), ::tolower);
cout<<str;
/*for(i=0;i<s.length();i++)
{
s[i]=toupper(s[i]);
}*/
}
return 0;
}
i wrote this code to convert to lower case but when run on ideone with input
1
hola please!!!
it shows output no can u tell or correct it morever this will help me learn the use of std:lowercase function taking getline cin as input rather than considering it as array

Answer 1

The problem is definitely with the way you are reading in. scanf("%d",&t); doesn't consume the return character, so it is still there on the getline, which will get an empty sting. Change it to scanf("%d\r",&t).

Answer 2

If you simplify the code, the problem can be reduced to:
int main() {
int t;
scanf("%d",&t);
std::string str;
std::getline(cin, str);
std::cout<<str;
}
This is because scanf reads from the input until it reaches a character that doesn't match, and it leaves that character in the input buffer. You input is "1\nhola please!\n\0", so scanf reads the 1, and leaves the rest: "\nhola please!\n\0". Then, you tell it to read until the next \n is found, which is immediately, so it returns an empty string.
The solution is: after using std::cin >> or scanf or whatever, if the next thing you want to do is read the rest of the line, you want to ignore that leading newline character. The C++ way to do this is std::cin.ignore(0xFFFFFFFF,'\n');, which will ignore the rest of the line. Alternatively, use scanf("%d\n" &t); to get the scanf to read in the newline character.
Related, you never check the validity of any of your input:
int main() {
int num_lines=0; //variables on different lines and initialized
std::cin >> num_lines
if (!std::cin)
return 1;
std::string str;
for(int j=0; j<num_lines && std::getline(sd::cin, str); ++j) {
std::transform(str.begin(), str.end(), str.begin(), ::tolower);
std::cout << str;
}
return 0;
}

Answer 3

Or simply use < boost/algorithm/string.hpp > header and function boost::to_lower().
int t = 0;
scanf("%d",&t);
std::cin.ignore();
while(t--) {
std::string str;
std::getline(cin, str);
boost::to_lower(str);
std::cout << str << std::endl;
}