Write a C program to read Octal number from user and convert to Decimal number system. How to convert from Octal number system to Decimal number system in C programming. Logic to convert octal to decimal number system in C program.

**Example**

**Input**

Input octal number: 172

**Output**

Decimal number: 122

## Required knowledge

Additional programming knowledge required for this program

## Octal number system

Octal number system is a base 8 number system. Octal number system uses 8 symbols to represent all its numbers i.e. 01234567

## Decimal number system

Decimal number system is a base 10 number system. Decimal number system uses 10 symbols to represent all its numbers i.e. 0123456789

## Algorithm to convert from octal to decimal

Algorithm Conversion Octal to Binarybegin:read(octal);decimal← 0;rem← 0;place← 0;While(octal!=0)begin:rem←octal% 10;decimal←decimal+ (8^{place}*rem);octal←octal/ 10;place←place+ 1;end;write('Decimal ='decimal);end;

## Program to convert octal to decimal

/** * C program to convert Octal number system to Decimal number system */ #include <stdio.h> #include <math.h> int main() { long long octal, tempOctal, decimal; int rem, place; /* * Input octal number from user */ printf("Enter any octal number: "); scanf("%lld", &octal); tempOctal = octal; decimal = 0; place = 0; /* * Convert octal to decimal */ while(tempOctal > 0) { // Extract the last digit of octal rem = tempOctal % 10; // Convert last octal digit to decimal decimal += pow(8, place) * rem; // Remove the last octal digit tempOctal /= 10; place++; } printf("Octal number = %lld\n", octal); printf("Decimal number = %lld", decimal); return 0; }

Enter any octal number: 172 Octal number = 172 Decimal number = 122

Happy coding ;)

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