[RESOLVED] Adding char to beginning of string

[BytePtr]

I have variable that is sometimes like 2 digits, but sometimes it goes to 1 digit, like 0, 1, 2 etc.
And when it's < 2 then i need to add zero (char) before it so it will look like 01, 02 etc.
I know strcat can merge strings but it can add strings(chars) only at the end of char. but i need to add to the beginning of string or char.
Im using Borland C++ 3.1. There is strnset and i can add char with this to beginning but it erases number that i have (1, 2, 3 etc) (almost useless function).
I made same app in Pascal, there was so easy:

if length(var1) < 2 then var1:='0' + var1

but C++ don't accept this, so all i need to know how to do this '0' + var1 in C++.
If somebody knows how to solve this then plz let me know. Im searching in Google also.
Any hints or tips are welcome.

thx in advance.

[wildfrog]

Like this?

const char pcszUnfixed[] = "5";
char* pszFixed;

if (strlen(pcszUnfixed) < 2)
{
    // prefix string with '0'
    pszFixed = new char[strlen(pcszUnfixed) + 2];
    strcpy(pszFixed, "0");
    strcat(pszFixed, pcszUnfixed);
} else
{
    // just make a copy of the original string
    pszFixed = strdup(pcszUnfixed);
}

// print string
printf("%s --> %s\n", pcszUnfixed, pszFixed);

// clean up
delete[] pszFixed;

- petter

[olivthill]

Another way to do it is:

char var1[3];
if (strlen(var1) < 2) {
   strcpy(&var1[1], &var[0]);
   var1[0] = '0';
}

I don't use "new", because I presume that your variable is declared with a length of at least three characters, otherwise it wouldn't be able to contain 2-digit-numbers.

[wien]

I made same app in Pascal, there was so easy:

if length(var1) < 2 then var1:='0' + var1

but C++ don't accept this, so all i need to know how to do this '0' + var1 in C++.

This is just as easy in C++.

#include <string>
...
std::string var1("4");

if(var1.length() < 2)
    {
    var1 = '0' + var1;
    }

[NMTop40]

Pretty sure it can be done with streams. Set the width to 2 and the padding to '0'?

Anyway, that is assuming we start with something other than a string. But if we already startr with a string then:

if (s.size() < 2 )
{
   s.insert(0, '0' );
}

[BytePtr]

Thanks alot for all, i will try this all out and post results.

[Bond]

If you're just using character arrays, sprintf can make things easy:

char szResult[3];   // two digits plus null
sprintf(szResult, "%02s", szNumber);

This will always return a two-character string with a leading zero, if needed, so you don't need to test for length < 2 (unless you want to).

[BytePtr]

Bond it can be make simpler but i need later this variable in graphics mode. Output will be made with: outtext().
And sprintf cannot output text in graphics mode.
Thx anyway. I will write this hint down for future.

[stober]

This will always return a two-character string with a leading zero, if needed, so you don't need to test for length < 2 (unless you want to).

That's not correct. the 2 in %02s is only the MINUMUM number of characters, not the maximum or exact number. if szNumber is your example is "1234", then the result of that sprintf will be "1234". Example:

int main() 
{ 
	char szNumber[] = "1234";
	char buf[8];
	sprintf(buf,"%02s",szNumber);
	printf("%s\n",buf);
	return 0;
}

[HighCommander4]

There is a very simple solution:

#include <iostream>
#include <iomanip>

int number;  // can be 1 or 2 digits
cout << setw(2) << number;   // will output a preceding zero if it's one digit

If you need to store the number in a string, you can use an ostringstream object instead of cout.

[stober]

Bond it can be make simpler but i need later this variable in graphics mode. Output will be made with: outtext().
And sprintf cannot output text in graphics mode.
Thx anyway. I will write this hint down for future.

The text has to be formatted somehow before you can send it to any GUI function for diplay. sprintf() is just doing that formatting, and you have to call other functions to display the string.

[Bond]

That's not correct. the 2 in %02s is only the MINUMUM number of characters, not the maximum or exact number. if szNumber is your example is "1234", then the result of that sprintf will be "1234".

You are correct. Based on his original question where he states it will be "sometimes 2, but also sometimes 1" and the fact that he only wants to pad the number to fill a two-character field, I was assuming that the number would always be one or two digits. I may have misunderstood.

Thanks.

[BytePtr]

Only working solution that i have worked out is to display zero as char or string if length of variable is less than 2 else display as usually.
I got it working with strcat but i must work out normal program flow so it will call strcat only when length < 2. i guess i must make some function or procedure. it works now but im getting overflow and windows diplays errors. Yeah it's clock stuff.

#include <conio.h>
#include <dos.h>
#include <string.h>
#include <stdlib.h>
#include <iostream.h>

int main(void)

{
	clrscr();

	struct time t;

	int sekund;
	char *sek;
	char *null="0";

	while(!kbhit())
	{
	gettime(&t);
	sekund = t.ti_sec;
	itoa(sekund, sek, 10);

	if(strlen(sek) < 2)
	{
		strcat(null, sek);
		gotoxy(3,3);
		delay(1000);
		clrscr();
		cprintf(null);
	}
	else
	{
		gotoxy(3,3);
		delay(1000);
		clrscr();
		cprintf(sek);
	}
	}


	getch();
	return 0;
}

Problem is that program calls strcat every second if length < 2 b(thats why overwflows) but i need to call it only once if length < 2 and display zero until its needed. Thats why i must work out right program flow. maybe using some goto's. but it's bad.

[stober]

re-read post #7, Bond already showed you an easy way to do it. Its not necessary to check for string length.

[thre3dee]

edit** check my next post