Write a C program to read Hexadecimal number from user and convert it to Octal number system. How to convert Hexadecimal number system to Octal number system in C programming. Logic to convert hexadecimal number to octal number system in C program.

**Example**

**Input**

Input hexadecimal: 1A

**Output**

Octal number: 32

## Required knowledge

Must have programming knowledge before this program.

## Hexadecimal number system

Hexadecimal number system is a base 16 number system. It uses 16 symbols to represent all numbers i.e. 0123456789ABCDEF

## Octal number system

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

## Algorithm to convert hexadecimal to octal

There isn't any easy and direct conversion algorithm from hexadecimal to octal number system. Below is the step by step descriptive logic to convert hexadecimal to decimal number system.

- Convert the given hex number to equivalent binary.
- Group the converted binary in groups of 3 bits.
- Write the corresponding octal value of for each grouped binary number digit.

**Binary to Octal conversion table**

Decimal | Binary | Octal |

0 | 000 | 0 |

1 | 001 | 1 |

2 | 010 | 2 |

3 | 011 | 3 |

4 | 100 | 4 |

5 | 101 | 5 |

6 | 110 | 6 |

7 | 111 | 7 |

## Program to convert hexadecimal to octal

/** * C program to convert Hexadecimal to Octal number system */ #include <stdio.h> int main() { char hex[17]; long long octal, bin, place; int i = 0, rem, val; /* * Input hexadecimal number from user */ printf("Enter any hexadecimal number: "); gets(hex); octal = 0ll; bin = 0ll; place = 0ll; /* * Hexadecimal to binary conversion */ for(i=0; hex[i]!='\0'; i++) { bin = bin * place; switch(hex[i]) { case '0': bin += 0; break; case '1': bin += 1; break; case '2': bin += 10; break; case '3': bin += 11; break; case '4': bin += 100; break; case '5': bin += 101; break; case '6': bin += 110; break; case '7': bin += 111; break; case '8': bin += 1000; break; case '9': bin += 1001; break; case 'a': case 'A': bin += 1010; break; case 'b': case 'B': bin += 1011; break; case 'c': case 'C': bin += 1100; break; case 'd': case 'D': bin += 1101; break; case 'e': case 'E': bin += 1110; break; case 'f': case 'F': bin += 1111; break; default: printf("Invalid hexadecimal input."); } place = 10000; } place = 1; /* * Binary to octal conversion */ while(bin > 0) { rem = bin % 1000; switch(rem) { case 0: val = 0; break; case 1: val = 1; break; case 10: val = 2; break; case 11: val = 3; break; case 100: val = 4; break; case 101: val = 5; break; case 110: val = 6; break; case 111: val = 7; break; } octal = (val * place) + octal; bin /= 1000; place *= 10; } printf("Hexadecimal number = %s\n", hex); printf("Octal number = %lld", octal); return 0; }

Enter any hexadecimal number: fff Hexadecimal number = fff Octal number = 7777

Happy coding ;)

### Recommended posts

- Loop programming exercises and solutions in C.
- C program to convert Hexadecimal to Binary number system.
- C program to convert Hexadecimal to Decimal number system.
- C program to convert Binary to Octal number system.
- C program to convert Octal to Hexadecimal number system.
- C program to convert Decimal to Octal number system.

< pre>< code >----Your Source Code---- < / code > < / pre > (Remove spaces from pre and code tags)