#include<stdio.h>
#define MAX 1000

int main(){
    char binaryNumber[MAX],hexaDecimal[MAX];
    long int i=0;

    printf("Enter any hexadecimal number: ");
    scanf("%s",hexaDecimal);

    printf("\nEquivalent binary value: ");
    while(hexaDecimal[i]){
         switch(hexaDecimal[i]){
             case '0': printf("0000"); break;
             case '1': printf("0001"); break;
             case '2': printf("0010"); break;
             case '3': printf("0011"); break;
             case '4': printf("0100"); break;
             case '5': printf("0101"); break;
             case '6': printf("0110"); break;
             case '7': printf("0111"); break;
             case '8': printf("1000"); break;
             case '9': printf("1001"); break;
             case 'A': printf("1010"); break;
             case 'B': printf("1011"); break;
             case 'C': printf("1100"); break;
             case 'D': printf("1101"); break;
             case 'E': printf("1110"); break;
             case 'F': printf("1111"); break;
             case 'a': printf("1010"); break;
             case 'b': printf("1011"); break;
             case 'c': printf("1100"); break;
             case 'd': printf("1101"); break;
             case 'e': printf("1110"); break;
             case 'f': printf("1111"); break;
             default:  printf("\nInvalid hexadecimal digit %c ",hexaDecimal[i]); return 0;
         }
         i++;
    }

    return 0;
}
Sample output:
Enter any hexadecimal number: 2AD5
Equivalent binary value: 0010101011010101

#include<stdio.h>
int main(){
   
    long int binaryNumber,octalNumber=0,j=1,remainder;

    printf("Enter any number any binary number: ");
    scanf("%ld",&binaryNumber);

    while(binaryNumber!=0){
         remainder=binaryNumber%10;
        octalNumber=octalNumber+remainder*j;
        j=j*2;
        binaryNumber=binaryNumber/10;
    }

    printf("Equivalent octal value: %lo",octalNumber);

    return 0;
}
Sample output:
Enter any number any binary number: 1101
Equivalent hexadecimal value: 15

#include<stdio.h>
#define MAX 1000

int main(){
   
    char binaryNumber[MAX],octalNumber[MAX];
    long int i=0,j=0;

    printf("Enter any number any binary number: ");
    scanf("%s",binaryNumber);

    while(binaryNumber[i]){
      binaryNumber[i] = binaryNumber[i] -48;
      ++i;
    }

    --i;
    while(i-2>=0){
    octalNumber[j++] = binaryNumber[i-2] *4 +  binaryNumber[i-1] *2 + binaryNumber[i] ;
    i=i-3;
    }

    if(i ==1)
      octalNumber[j] = binaryNumber[i-1] *2 + binaryNumber[i] ;
    else if(i==0)
      octalNumber[j] =  binaryNumber[i] ;
    else
      --j;

    printf("Equivalent octal value: ");
    while(j>=0){
      printf("%d",octalNumber[j--]);
    }

    return 0;
}
Sample output:
Enter any number any binary number: 1111111111111111111
1111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111
11111111
Equivalent octal value: 3777777777777777777777777777777
7777777777777777777777777777777777777777777777777777

#include<stdio.h>

int main(){
   
    long int binaryNumber,decimalNumber=0,j=1,remainder;

    printf("Enter any number any binary number: ");
    scanf("%ld",&binaryNumber);

    while(binaryNumber!=0){
         remainder=binaryNumber%10;
        decimalNumber=decimalNumber+remainder*j;
        j=j*2;
        binaryNumber=binaryNumber/10;
    }

    printf("Equivalent decimal value: %ld",decimalNumber);

    return 0;
}
Sample output:
Enter any number any binary number: 1101
Equivalent decimal value: 13

#include<stdio.h>
int main(){
   
    long int binaryNumber,hexadecimalNumber=0,j=1,remainder;
   
    printf("Enter any number any binary number: ");
    scanf("%ld",&binaryNumber);
   
    while(binaryNumber!=0){
    remainder=binaryNumber%10;
    hexadecimalNumber=hexadecimalNumber+remainder*j;
        j=j*2;
        binaryNumber=binaryNumber/10;
      }
   
    printf("Equivalent hexadecimal value: %lX",hexadecimalNumber);

    return 0;
}
Sample output:
Enter any number any binary number: 1101
Equivalent hexadecimal value: D