C Program to Convert Hexadecimal Number to Octal Number System

Write a C program to read a hexadecimal number and convert hexadecimal number to octal number system.
Wap in C to convert a base 16 number to a base 8 number.

Required Knowledge

• C printf and scanf functions
• For loop in C

This program converts a hexadecimal number( base 16) to octal number (base 8). Hexadecimal number system is a base 16 number system using digits 0 to 9 and A to F, whereas Octal number system is base 8 and using digits from 0 to 7. Given a hexadecimal number as input from user convert it to octal number.

For Example

12D in Hexadecimal is equivalent to 455 in Octal number system.
Here, we will first convert hexadecimal number to binary number then binary number to octal number system.

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C program to convert a hexadecimal number to octal number

#include <stdio.h>  
#include <string.h>  
  
int main() {  
    int hexDigitToBinary[16] = {0, 1, 10, 11, 100, 101, 110, 111,
      1000, 1001, 1010, 1011, 1100, 1101, 1110, 1111};     
    char hexDigits[16] = {'0', '1', '2', '3', '4', '5', '6', '7',
      '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
    int octalDigitToBinary[8] = {0,1,10,11,100,101,110,111}; 
    char hexadecimal[30];
    long long binaryNumber =0, octalNumber;   
    int i = 0, j, index=0, multiple = 1, threeDigits;  
  
    /* 
     * Take a hexadecimal number as input from user 
     */  
    printf("Enter a Hexadecimal Number\n");  
    scanf("%s", hexadecimal);
    
    /* First Convert Hexadecimal Number to Binary Numbers
     * Find he hexadecimal digit in hexDigits and the substitute it
  * with corresponding value in hexDigitToBinary
     */
    
    for(i=0; hexadecimal[i] != '\0'; i++)  {  
        /*Search through hexDigits array */
        for(j = 0; j < 16; j++){
          if(hexDigits[j] == hexadecimal[i]){
            binaryNumber = binaryNumber*10000 + hexDigitToBinary[j];
          }
        }
    }  
    /* 
     * Now Convert Binary Number to Octal Number   
     */   
    while(binaryNumber != 0) {  
        threeDigits = binaryNumber % 1000;
        /*Search through octalDigitToBinary array */
        for(i = 0; i < 8; i++) {  
            if(octalDigitToBinary[i] == threeDigits) {  
                octalNumber = (i * multiple) + octalNumber;  
                break;  
            }  
        }  
        /* Remove last three digits */
        binaryNumber = binaryNumber/1000;  
        multiple *= 10;  
    }  
    printf("Octal Mumber : %ld", octalNumber);  
  
    return 0;  
}

Output

Enter a Hexadecimal Number
12D
Octal Mumber : 455

Enter a Hexadecimal Number
1
Octal Mumber : 1