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Join Date: Dec 2004

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dannyfang

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String to integer conversion

Dec 13th, 2004

Hi,

I'm a freshman in computer science and a new member to this forum. I'd like to convert the string representation of a number e.g "456" into its integer equivalent i.e. 456.

As for character representation of single digits e.g. "6", I'm able to convert it to its integer equivalent by doing:
char myChar = "6";
int asciiVal = myChar - '0'; //produces the integer 6 now.

Could anyone show me how the string representation of a number like "456" can be converted to its integer equivalent?

Thanks
Danny

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jwenting

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Re: String to integer conversion

Dec 13th, 2004

there's a function to do just that in the standard library by the name of atoi (ASCII to Integer).

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thatsalok

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Re: String to integer conversion

Dec 13th, 2004

Use it this Way

char a[]="123";
char b[]="123.66";
//for interger
int i=atoi(a);

//for Long

long l=atol(a);

//for double

float d=atof(b);

Hope this will help you

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------------------------
Regard's
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visit me at http://www.thisisalok.tk

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Dave Sinkula Dave Sinkula is offline

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long time no c

Re: String to integer conversion

Dec 13th, 2004

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Originally Posted by dannyfang

Could anyone show me how the string representation of a number like "456" can be converted to its integer equivalent?

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#include <stdio.h>

int main(void)
{
   int i, value;
   const char text[] = "456";
   for (i = 0, value = 0; text [ i ] != '\0'; ++i)
   {
      value *= 10;
      printf("value *= 10 = %3d, ", value);
      value += text [ i ] - '0'; /* add value of current digit character */
      printf("value += '%c' - '0' = %3d\n", text [ i ], value);
   }
   return 0;
}

/* my output
value *= 10 =   0, value += '4' - '0' =   4
value *= 10 =  40, value += '5' - '0' =  45
value *= 10 = 450, value += '6' - '0' = 456
*/

[edit]Or another way of looking at it:

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#include <stdio.h>

int main(void)
{
   int i, value;
   const char text[] = "456";
   for ( i = 0, value = 0; text [ i ] != '\0'; ++i )
   {
      int digit = text [ i ] - '0'; /* get value of current digit character */
      printf("value = %3d, %3d * 10 = %3d, ", value, value, value * 10);
      value = 10 * value + digit;
      printf("digit = %d, value = %d\n", digit, value);
   }
   return 0;
}

/* my output
value =   0,   0 * 10 =   0, digit = 4, value = 4
value =   4,   4 * 10 =  40, digit = 5, value = 45
value =  45,  45 * 10 = 450, digit = 6, value = 456
*/

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Join Date: Dec 2004

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dannyfang

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Re: String to integer conversion

Dec 14th, 2004

Dave, Alok & Jwenting,

Thanks very much for the help. In fact I forgot to mention earlier when posting this problem that I'm not suppose to use built-in functions like atoi or atol for such conversions. Nevertheless, thanks to everyone for their help.

Dave,
Your solution provided the answer to my problem. thanks.

Danny.

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1o0oBhP

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Re: String to integer conversion

Dec 15th, 2004

whilst we're on the subject is there a lib function for integer to string ect....

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cameronius cameronius is offline

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Re: String to integer conversion

Jan 30th, 2005

i tried the method above, but the segmentation fault error kept appearing.

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Dave Sinkula Dave Sinkula is offline

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long time no c

Re: String to integer conversion

Jan 30th, 2005

You're not passing a valid string to atol.

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murschech

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Re: String to integer conversion

Jan 30th, 2005

•

Originally Posted by 1o0oBhP

whilst we're on the subject is there a lib function for integer to string ect....

Yes. itoa is the name of the function. There are corresponding functions for long or double to string. Here's an example.

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
#include <stdlib.h>
#include <iostream.h>
 
main()
{    int val;
      char st[10]
 
        val = 5 + 10;
        itoa(val,st,10) //base 10
        cout <<"decimal: "<<st<<endl;
        itoa(val,st,16)  //hexidecimal
        cout <<"hexidecimal: "<< st << endl;
}
#include <stdlib.h>
#include <iostream.h>

main()
{    int val;
      char st[10]
 
        val = 5 + 10;
        itoa(val,st,10) //base 10
        cout <<"decimal: "<<st<<endl;
        itoa(val,st,16)  //hexidecimal
        cout <<"hexidecimal: "<< st << endl;
}