Convert Integer to String and String to Integer

**hqt** · 09-15-2011

I am willing to bet you are getting an error at the line below that, when you try to use printf to print a string object to the screen

Oh, you say right, .... and I'm say right too. Because, It's very funny and I don't know why. I will explain, now:
first code:

Code:

#include<iostream>
#include<string>
#include<stdio.h>
#include<sstream>
using namespace std;
int main(){
	int number=567;
	string myphrase;
	stringstream ss(stringstream::in | stringstream::out);
 	ss<<number;
	myphrase = "your number is " + ss.str();
 }

this code is NO ERROR.
and this is my second code:

Code:

#include<iostream>
#include<string>
#include<stdio.h>
#include<sstream>
using namespace std;
int main(){
	int number=567;
	string myphrase;
	stringstream ss(stringstream::in | stringstream::out);
 	ss<<number;
	myphrase = "your number is " + ss.str();//--> I use debugger and see that error from this line, mean it's not run line "printf" yet.
        /* ************************** */
        printf("%s\n",str);
}

So, I don't know how your compiler is, I'm using Code::Block, and I cannot answer why

2) and answer to your question, why I prefer printf/scanf than cint/cout because printf/scanf run faster than cint/cout. It's pretty sure because:
a) my teacher say that
b) many document say that,too
c) my experience: there a problem on SPOJ, I must read N^2 element (N=10^9), if I use printf/scanf I will pass my test, and if I use cint/cout, It's not

that why, I always try to use old function from C

so, who can answer for me above questions, please.
thanks for ton

**Elysia** · 09-15-2011

Originally Posted by hqt

2) and answer to your question, why I prefer printf/scanf than cint/cout because printf/scanf run faster than cint/cout. It's pretty sure because:
a) my teacher say that
b) many document say that,too
c) my experience: there a problem on SPOJ, I must read N^2 element (N=10^9), if I use printf/scanf I will pass my test, and if I use cint/cout, It's not

that why, I always try to use old function from C

so, who can answer for me above questions, please.
thanks for ton

Then your teacher is misguided because that is not true.

**AndrewHunter** · 09-15-2011

Originally Posted by hqt

So, I don't know how your compiler is, I'm using Code::Block, and I cannot answer why

Neither can I at the moment.

Originally Posted by hqt

2) and answer to your question, why I prefer printf/scanf than cint/cout because printf/scanf run faster than cint/cout. It's pretty sure because:
a) my teacher say that
b) many document say that,too
c) my experience: there a problem on SPOJ, I must read N^2 element (N=10^9), if I use printf/scanf I will pass my test, and if I use cint/cout, It's not

that why, I always try to use old function from C

so, who can answer for me above questions, please.
thanks for ton

If you want to run C code, program in C not in C++. I have not heard of cin/cout being slower than printf and scanf, so I will save that discussion for someone else.

If the code I posted does not compile for you, you need to post the specific error messages so we can figure out why.

**hqt** · 09-15-2011

No no, the code you post is right, no problem

but the code of mine, is wrong, and the secret is: I know that problem from that line, but when I still not run to that line, It meet problem

**Elkvis** · 09-15-2011

you are getting errors because you are trying to use printf() to print a C++ string (std::string). you cannot do that. use cout. do not mix C and C++ console I/O, as they are not guaranteed to be compatible, and you may get unexpected (ugly) output if you mix them.

cout is not slower than printf. this may have been true in the early days of C++, before there were highly optimized C++ compilers and libraries, and when C compilers and libraries were already very mature, but it is certainly false now.

**laserlight** · 09-15-2011

Originally Posted by hqt

I use debugger and see that error from this line, mean it's not run line "printf" yet.

You probably just misread the debugger's output. AndrewHunter is correct. The %s format specifier for printf applies to null terminated C-style strings, not std::string objects.

Originally Posted by hqt

2) and answer to your question, why I prefer printf/scanf than cint/cout because printf/scanf run faster than cint/cout. It's pretty sure because:
a) my teacher say that
b) many document say that,too

It is true that C++ I/O stream operations tend to be slower than their C counterparts because they may involve some extra work. On the other hand, this extra work can bring about safety and ease of usage (though the syntax may actually become more verbose, heh), and typically does not actually matter in the bigger picture.

Originally Posted by hqt

c) my experience: there a problem on SPOJ, I must read N^2 element (N=10^9), if I use printf/scanf I will pass my test, and if I use cint/cout, It's not

That is fine: if you find that you need to use the C-style I/O for special reasons, go ahead. But generally, default to C++-style I/O in C++.

**hqt** · 09-15-2011

Sorry, because my document not in English (of course, because I'm not in country that speak English

, so I must find another source that give this:
this is first:RootTalk: cint FAQ

In most cases cint runs fast, but a small change makes it very slow. Why?
Cint uses incremental bytecode compilation technique. The bytecode compiler
has size and syntax limitations. When you hit that limitation, cint runs
10-20 times slower.

this is second:
cin or scanf???
you should see mariam.kupa post, he have same idea with me

and many of my friend say that. of course, It just a little, but if you read 10^9^2 element, different will about 1-2 seconds (to cost !!!, because a program must run in that time

)

**laserlight** · 09-15-2011

Originally Posted by hqt

this is first:RootTalk: cint FAQ

That FAQ is irrelevant as it is about a C++ interpreter, not about C++ I/O streams.

**hqt** · 09-15-2011

Oh, std::string cannot use with printf/scanf

Simple, but maybe enough for me

and, I may have last question in this topic: I don't know purpose of stringstream, so who can explain it shortly for me, please. (In my mind, I don't think it just only to convert from integer to string

)

@laserlight: uhm, I think your have same time zone with me, I meet you at this early morning, and now, I meet you again

**laserlight** · 09-15-2011

Originally Posted by hqt

I don't know purpose of stringstream, so who can explain it shortly for me, please. (In my mind, I don't think it just only to convert from integer to string

Its purpose is to deal with strings as if they were I/O streams, hence the kind of operations available for I/O streams would be available, in a way, with strings. You may be familiar with sprintf, which has a similiar idea.

Originally Posted by hqt

@laserlight: uhm, I think your have same time zone with me, I meet you at this early morning, and now, I meet you again

GMT+8

**hqt** · 09-15-2011

Oh, convert from pascal to C have some strange points, and from C to C++, I cannot imagine :-O
Now, I'm thinking about Perl, the most freedom language I have learnt :">

**Alexandre** · 09-15-2011

laserlight lives in the future ! Hi from the past !

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