C Program to Convert Octal Number to Binary Number System

C program to convert octal number to binary number system. Binary number system is a base 2 number system using digits 0 and 1 whereas Octal number system is base 8 and using digits from 0 to 7. Given an octal number as input from user convert it to binary number.

For Example:
1203 in Octal is equivalent to 1010000011 in Binary number system.

Required Knowledge

Algorithm to convert Octal to Binary number
  • Create a mapping between octal digits and binary sequence {(0 => 000), (1 => 001), (2 => 010), (3 => 011), (4 => 100), (5 => 101), (6 => 110), (7 => 111)}
  • Now, replace each octal digit with it's corresponding binary sequence as mentioned above.

For Example:
Octal number : 1203
replace 1 by (001), 2 by (010), 0 by (000) and 3 by (011)
Decimal number = 001010000011 = 1010000011

C program to convert a octal number to binary number

#include <stdio.h>  
  
int main() {  
    int octalDigitToBinary[8] = {0, 1, 10, 11, 100, 101, 110, 111};  
    long long octalNumber, binaryNumber = 0, position;  
    int digit;  
      
    /* Take an Octal Number as input from user */  
    printf("Enter an Octal Number\n");  
    scanf("%ld", &octalNumber); 
  
    position = 1;  
    /* Convert Octal Number to Binary Number */  
    while(octalNumber != 0) {
        digit = octalNumber % 10;
        binaryNumber = (octalDigitToBinary[digit] * position) + binaryNumber;  
        octalNumber /= 10;  
        position *= 1000;  
    }

    printf("Binary Number = %ld", binaryNumber);
    
    return 0;
} 
Output
Enter an Octal Number
1203
Binary Number = 1010000011
Enter an Octal Number
1111
Binary Number = 1001001001

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