C++ Program to Extract Numbers from a String

This article provides some programs in C++ to extract all the numbers available in a string entered by the user at run-time. These are the lists of programs available in this article:

• Extract numbers from a string using a character array
• Extract numbers from a string using an integer array

Extract numbers from a string using a character array

The question is: write a program in C++ to extract and print numbers available in a string. The string must be entered by the user. The program given below is its answer:

#include<iostream>
#include<stdio.h>
#include<string.h>

using namespace std;
int main()
{
   char str[100], num[100];
   int tot, i, j=0;
   cout<<"Enter the String: ";
   gets(str);
   tot = strlen(str);
   for(i=0; i<tot; i++)
   {
      if(str[i]>='0' && str[i]<='9')
      {
         num[j] = str[i];
         j++;
      }
   }
   cout<<endl<<"Numbers extracted from the String:"<<endl;
   for(i=0; i<j; i++)
      cout<<num[i]<<" ";
   cout<<endl;
   return 0;
}

The snapshot given below shows the initial output produced by the above C++ program on extracting all the numbers available in a string entered by the user:

Now supply the input, say Hey 012, this is 394 from 329 fresherearth as a string. Press the ENTER key to extract and print all numbers available in the string as shown in the snapshot given below:

Extract numbers from a string using an integer array

This program does the same job as the previous program, but this program uses an integer array instead of a character array to do the job.

#include<iostream>
#include<stdio.h>
#include<string.h>

using namespace std;
int main()
{
   char str[100];
   int tot, i, j=0, num[100];
   cout<<"Enter the String: ";
   gets(str);
   tot = strlen(str);
   for(i=0; i<tot; i++)
   {
      if(str[i]>='0' && str[i]<='9')
      {
         num[j] = str[i];
         num[j] = num[j] - 48;
         j++;
      }
   }
   if(j==0)
      cout<<"\nNumber not found in the string!";
   else if(j==1)
   {
      cout<<"\nOnly one number found in the string:";
      cout<<endl<<num[0];
   }
   else
   {
      cout<<"\nAll numbers extracted from the string.\n";
      cout<<"\nThe list of Numbers are:"<<endl;
      for(i=0; i<j; i++)
         cout<<num[i]<<" ";
   }
   cout<<endl;
   return 0;
}

Here is its sample run with user input fresherearth as a string:

Here is another sample run with user input codes0123cracker9 as a string:

Note that the statement num[j] = num[j] - 48 is used in the preceding program to convert the ASCII value to its equivalent character (a number).

Note: The ASCII value of 0 is 48, 1 is 49, 2 is 50, ..., and 9 is 57. This means that you can get the number by subtracting 48 from the ASCII value.

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