# Function to determine the length of an integer string

Discussion in 'C++' started by coinjo, Dec 7, 2005.

1. ### coinjoGuest

Is there any function to determine the length of an integer string?

coinjo, Dec 7, 2005

2. ### Ravi SrivastavaGuest

strlen gives the length of string irrespective of its content (ie.
integer or character)

Ravi Srivastava, Dec 7, 2005

3. ### Guest

coinjo wrote:
> Is there any function to determine the length of an integer string?

What is an integer string?

std::string has a function that returns its length.

If you have a variable of any of the integer types, you can turn the
number it represents into a string using a stringstream (you can even
choose decimal, hexadecimal or octal representation by using the
appropriate stream manipulators). Once you've done that, you can ask
the string how long it is.

If none of that helps, post some code to show what you are trying to
do.

Gavin Deane

, Dec 7, 2005
4. ### GregGuest

coinjo wrote:
> Is there any function to determine the length of an integer string?

Take the logrithm of the value (rounded down to an integer) then add
one.

Note that the base of the logrithm has to match the base used to
represent the value. For example, if the number is 100 decimal, the
equation would be:

Log10(100)+1 = 3

so 100 has 3 digits as a decimal number.

Greg

Greg, Dec 7, 2005
5. ### coinjoGuest

#include<iostream>
#include<fstream>
using namespace std;

void selectionSort(int list[], int length)
{
int index;
int smallestIndex;
int minIndex;
int temp;

for(index=0; index<length-1; index++)
{
smallestIndex=index;

for(minIndex=index+1; minIndex<length; minIndex++)
if(list[minIndex]<list[smallestIndex])
smallestIndex=minIndex;
temp=list[smallestIndex];
list[smallestIndex]=list[index];
list[index]=temp;
}
};

int main()
{
int s[100];
int c=0;
int count=0;
ifstream a;
a.open("in.txt");

selectionSort(s,10);

while(a>>s[count] && !a.eof())
{
count++;
}

c=strlen(s);
return 0;
}

in.txt contains:
9
8
7
6
5
4
3
2
1

whether i include cstring file or not i get an error message in vc++;
(40) : error C2664: 'strlen' : cannot convert parameter 1 from 'int
[100]' to 'const char *'
Types pointed to are unrelated; conversion requires
reinterpret_cast, C-style cast or function-style cast

coinjo, Dec 7, 2005
6. ### Guest

coinjo wrote:
> #include<iostream>
> #include<fstream>
> using namespace std;
>
> void selectionSort(int list[], int length)
> {

<snip contents of this function that operates on values in the list
array>

> };

Spurious semicolon. It can go.

> int main()
> {
> int s[100];
> int c=0;
> int count=0;
> ifstream a;
> a.open("in.txt");
>
> selectionSort(s,10);

There is nothing in s at the moment. What do you think selectionSort is
going to do? If it touches any of the uninitialised int varaibles in s
(which it does) then you have undefined behaviour. Which is bad.

> while(a>>s[count] && !a.eof())
> {
> count++;
> }
>
> c=strlen(s);

If we ignore the problem call to selectionSort, it looks like you have
an int array s with the first count elements holding the values read
from in.txt. And if I've understood, you want to know the total number
of digits in all those ints.

Using the technique posted by Greg, change you while loop to

int total_digits = 0;
while(a>>s[count] && !a.eof())
{
total_digits += log10(s[count]) + 1;
count++;
}

You'll need to #include<math.h> to get the log10 function. And note
that this will count decimal digits.

Gavin Deane

, Dec 7, 2005
7. ### Default UserGuest

coinjo wrote:

> whether i include cstring file or not i get an error message in vc++;
> (40) : error C2664: 'strlen' : cannot convert parameter 1 from 'int
> [100]' to 'const char *'
> Types pointed to are unrelated; conversion requires
> reinterpret_cast, C-style cast or function-style cast

The strlen() function works by searching the string for the special
text character '\0'. As 0 is a valid integer, and in no way special,
int arrays are not terminated in that way.

If size in important, either keep track of it or scrap arrays and use
vectors. At your level of skill, vectors are the better choice by far.

Brian

Default User, Dec 7, 2005
8. ### Jonathan McdougallGuest

coinjo wrote:
> #include<iostream>
> #include<fstream>
> using namespace std;

http://www.parashift.com/c++-faq-lite/coding-standards.html#faq-27.5

> void selectionSort(int list[], int length)
> {
> int index;
> int smallestIndex;
> int minIndex;
> int temp;

http://www.parashift.com/c++-faq-lite/coding-standards.html#faq-27.7

> for(index=0; index<length-1; index++)

> {
> smallestIndex=index;
>
> for(minIndex=index+1; minIndex<length; minIndex++)
> if(list[minIndex]<list[smallestIndex])
> smallestIndex=minIndex;
>
> temp=list[smallestIndex];
> list[smallestIndex]=list[index];
> list[index]=temp;

std::swap(list[smallestIndex], list[index]);

> }
> };
>
> int main()
> {
> int s[100];
> int c=0;
> int count=0;
> ifstream a;
> a.open("in.txt");

ifstream in("in.txt");

Use constructors and descriptive names.

> selectionSort(s,10);

Don't you want to sort *after* reading?

> while(a>>s[count] && !a.eof())

This will fail if the file contains something else than integers.

> {
> count++;
> }

You could also do

while (in >> s[count++])
;

std::sort(s, s+count);

> c=strlen(s);

See below.

> return 0;
> }
>
> in.txt contains:
> 9
> 8
> 7
> 6
> 5
> 4
> 3
> 2
> 1
>
> whether i include cstring file or not i get an error message in vc++;
> (40) : error C2664: 'strlen' : cannot convert parameter 1 from 'int
> [100]' to 'const char *'
> Types pointed to are unrelated; conversion requires
> reinterpret_cast, C-style cast or function-style cast

An "integer string" does not exist, it makes no sense. A string is a
sequence of characters, so that would be an "integer sequence of
characters". strlen() works with a sequence of char's, nothing else.
wcslen() works with a sequence of wchar_t's.

However, a sequence of ints may be a string (for example, an
implementation could have a character set, such as unicode, which would
be encoded on 32-bit unsigned ints), but in this case we would not call
this an "integer string" (because that's not what it is), but a "wide
character string" or something like that.

Semantically, you are not working on a "string", but on a container of
ints. Although both could be implemented the same way
(container-of-chars, container-of-ints), they are different.

IIUC, you want to determine the number of integers that were read from
the file (the "length" of your "string", or more specifically, the
number of elements in your container). You have several ways to do
that:

2) use a container

std::vector<int> v;

int temp=0;
while (in >> temp)
v.push_back(temp);

int count = v.length();

3) use an "end" value, such as 0

int s[100] = {0};

int count=0;
for (int i=0; s != 0; ++i)
++count;

But that will work only if 0 is not a valid value.

4) Embed the number of elements in the file (as the first line for
example)

Jonathan

Jonathan Mcdougall, Dec 7, 2005
9. ### coinjoGuest

#include<iostream.h>
#include<fstream>
#include<cstring>
#include<math.h>
using namespace std;

void selectionSort(int list[], int length)
{
int index;
int smallestIndex;
int minIndex;
int temp;

for(index=0; index<length-1; index++)
{
smallestIndex=index;

for(minIndex=index+1; minIndex<length; minIndex++)
if(list[minIndex]<list[smallestIndex])
smallestIndex=minIndex;
temp=list[smallestIndex];
list[smallestIndex]=list[index];
list[index]=temp;
}
};

void main()
{
int s[100];
int c=0;
int count=0;
ifstream a;
a.open("in.txt");

int total_digits = 0;

while(a>>s[count] && !a.eof())
{
total_digits += log10(s[count]) + 1;
count++;
}

count=0;

selectionSort(s,total_digits);

while(count<total_digits)
{
cout<<s[count]<<endl;
count++;
}
}

Thanks to all of you for your generous help, I now have come up with
this and as far as i thinks, it works! Please post any suggestions or
corrections (if there are any) to this.

coinjo, Dec 8, 2005
10. ### coinjoGuest

#include<iostream.h>
#include<fstream>
#include<cstring>
#include<math.h>
using namespace std;

void selectionSort(int list[], int length)
{
int index;
int smallestIndex;
int minIndex;
int temp;

for(index=0; index<length-1; index++)
{
smallestIndex=index;

for(minIndex=index+1; minIndex<length; minIndex++)
if(list[minIndex]<list[smallestIndex])
smallestIndex=minIndex;
temp=list[smallestIndex];
list[smallestIndex]=list[index];
list[index]=temp;
}
};

void main()
{
int s[100];
int c=0;
int count=0;
ifstream a;
a.open("in.txt");

int total_digits = 0;

while(a>>s[count] && !a.eof())
{
total_digits += log10(s[count]) + 1;
count++;
}

count=0;

selectionSort(s,total_digits);

while(count<total_digits)
{
cout<<s[count]<<endl;
count++;
}
}

Thanks to all of you for your generous help, I now have come up with
this and as far as i thinks, it works! Please post any suggestions or
corrections (if there are any) to this.

coinjo, Dec 8, 2005
11. ### coinjoGuest

#include<iostream.h>
#include<fstream>
#include<cstring>
#include<math.h>
using namespace std;

void selectionSort(int list[], int length)
{
int index;
int smallestIndex;
int minIndex;
int temp;

for(index=0; index<length-1; index++)
{
smallestIndex=index;

for(minIndex=index+1; minIndex<length; minIndex++)
if(list[minIndex]<list[smallestIndex])
smallestIndex=minIndex;
temp=list[smallestIndex];
list[smallestIndex]=list[index];
list[index]=temp;
}
};

void main()
{
int s[100];
int c=0;
int count=0;
ifstream a;
a.open("in.txt");

int total_digits = 0;

while(a>>s[count] && !a.eof())
{
total_digits += log10(s[count]) + 1;
count++;
}

count=0;

selectionSort(s,total_digits);

while(count<total_digits)
{
cout<<s[count]<<endl;
count++;
}
}

Thanks to all of you for your generous help, I now have come up with
this and as far as i thinks, it works! Please post any suggestions or
corrections (if there are any) to this.

coinjo, Dec 8, 2005
12. ### Jonathan McdougallGuest

coinjo wrote:

A single post would have done the job, you know.

> #include<iostream.h>

Non standard.

# include <iostream>

Seriously, this won't compile with a modern compiler. Visual C++ 8
rejects this.

> #include<fstream>
> #include<cstring>
> #include<math.h>

Prefer <cmath>

> using namespace std;
>
> void selectionSort(int list[], int length)
> {
> int index;
> int smallestIndex;
> int minIndex;
> int temp;

This is *not* a good way to program in C++. You have been given some
is "better".

> for(index=0; index<length-1; index++)
> {
> smallestIndex=index;
>
> for(minIndex=index+1; minIndex<length; minIndex++)
> if(list[minIndex]<list[smallestIndex])
> smallestIndex=minIndex;
> temp=list[smallestIndex];
> list[smallestIndex]=list[index];
> list[index]=temp;
> }
> };
>
> void main()

Illegal, main() returns an int.

> {
> int s[100];
> int c=0;
> int count=0;
> ifstream a;
> a.open("in.txt");
>
> int total_digits = 0;
>
> while(a>>s[count] && !a.eof())
> {
> total_digits += log10(s[count]) + 1;
> count++;
> }
>
> count=0;
>
>
> selectionSort(s,total_digits);

This won't work. For example, if each number has two digits and you
have 60 numbers, you'll read past the array. This should be

selectionSort(s, count);

but don't reset count to 0 before.

> while(count<total_digits)
> {
> cout<<s[count]<<endl;

Again, this is undefined behavior if total_digits is >= 100.

> count++;
> }
> }
>
>
> Thanks to all of you for your generous help, I now have come up with
> this and as far as i thinks, it works! Please post any suggestions or
> corrections (if there are any) to this.

Jonathan

Jonathan Mcdougall, Dec 8, 2005
13. ### Guest

, Dec 8, 2005
14. ### Default UserGuest

coinjo wrote:

> Thanks to all of you for your generous help, I now have come up with
> this and as far as i thinks, it works! Please post any suggestions or
> corrections (if there are any) to this.

Why did you ignore most of the advice given to you?

Brian

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