#include<stdio.h>
int main(){
    long int decimalNumber,remainder,quotient;
    int i=1,j,temp;
    char hexadecimalNumber[100];

    printf("Enter any decimal number: ");
    scanf("%ld",&decimalNumber);

    quotient = decimalNumber;

    while(quotient!=0){
         temp = quotient % 16;

      //To convert integer into character
      if( temp < 10)
           temp =temp + 48;
      else
         temp = temp + 55;

      hexadecimalNumber[i++]= temp;
      quotient = quotient / 16;
  }

    printf("Equivalent hexadecimal value of decimal number %d: ",decimalNumber);
    for(j = i -1 ;j> 0;j--)
      printf("%c",hexadecimalNumber[j]);

    return 0;
}
Sample output:
Enter any decimal number: 45
Equivalent hexadecimal value of decimal number 45: 2D

#include<stdio.h>
int main(){

  long int decimalNumber;

  printf("Enter any decimal number: ");
  scanf("%d",&decimalNumber);

  printf("Equivalent hexadecimal number is: %X",decimalNumber);

  return 0;
}
Sample output:
Enter any decimal number: 45
Equivalent hexadecimal number is: 2D

#include<stdio.h>
#define MAX 1000
int main(){
   
    char octalNumber[MAX];
    long int i=0;

    printf("Enter any octal number: ");
    scanf("%s",octalNumber);

    printf("Equivalent binary value: ");
    while(octalNumber[i]){
        switch(octalNumber[i]){
             case '0': printf("000"); break;
             case '1': printf("001"); break;
             case '2': printf("010"); break;
             case '3': printf("011"); break;
             case '4': printf("100"); break;
             case '5': printf("101"); break;
             case '6': printf("110"); break;
             case '7': printf("111"); break;
             default:  printf("\nInvalid octal digit %c ",octalNumber[i]); return 0;
    }
    i++;
 }

    return 0;
}
Sample output:
Enter any octal number: 123
Equivalent binary value: 001010011

#include<stdio.h>
#include<math.h>

int main(){
   
    long int octal,decimal =0;
    int i=0;

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

    while(octal!=0){
         decimal = decimal + (octal % 10) * pow(8,i++);
         octal = octal/10;
    }

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

   return 0;
}
Sample output:
Enter any octal number: 346
Equivalent decimal value: 230

#include<stdio.h>

int main(){
   
    long int octalNumber;

    printf("Enter any octal number: ");
    scanf("%o",&octalNumber);

    printf("Equivalent decimal number is: %d",octalNumber);

    return 0;
}
Sample output:
Enter any octal number: 17
Equivalent decimal number is: 15