Programming Logic:

To convert or change the octal number to binary number replace the each octal digits by a binary number using octal to binary chart.

For example take 25: Binary of 2 is 010 and Binary of 5 is 101.

Therefore binary of octal 25 is: 010101

Program to convert Octal to Binary C++:

#include<iostream>
using namespace std;
#define MAX 1000
int main()
{
    char octalNumber[MAX];
    long int i=0;
    cout<<"Enter any octal number: ";
    cin>>octalNumber;
    cout<<"Equivalent binary value: ";
    while(octalNumber[i])
    {
        switch(octalNumber[i])
    {
             case '0': cout<<"000";
             break;
             case '1': cout<<"001";
         break;
             case '2': cout<<"010";
         break;
             case '3': cout<<"011";
         break;
             case '4': cout<<"100";
         break;
             case '5': cout<<"101";
         break;
             case '6': cout<<"110";
         break;
             case '7': cout<<"111";
         break;
             default:  cout<<"nInvalid octal digit "<<octalNumber[i];
         return 0;
        }
        i++;
    }
    return 0;
}

OUTPUT: