Convert from any base to decimal and vice versa in C++

In this tutorial, we will be discussing a program to convert from any base to a decimal and vice versa.

For this we will be provided with an integer and its base. Our task is to convert the number to its decimal equivalent. Further we will also be performing the reverse of this procedure as well.

Example

Live Demo

#include <stdio.h>
#include <string.h>
//returning values of a character
int val(char c) {
   if (c >= '0' && c <= '9')
      return (int)c - '0';
   else
      return (int)c - 'A' + 10;
}
//converting number to decimal equivalent
int convert_decimal(char *str, int base) {
   int len = strlen(str);
   int power = 1;
   int num = 0;
   int i;
   for (i = len - 1; i >= 0; i--) {
      if (val(str[i]) >= base) {
         printf("Invalid Number");
         return -1;
      }
      num += val(str[i]) * power;
      power = power * base;
   }
   return num;
}
int main() {
   char str[] = "11A";
   int base = 16;
   printf("Decimal equivalent of %s in base %d is " " %d\n", str, base, convert_decimal(str, base));
   return 0;
}

Ouptut

Decimal equivalent of 11A in base 16 is 282

Now performing the reverse of the operation.

Example

Live Demo

#include <stdio.h>
#include <string.h>
//returning values of a character
char reVal(int num) {
   if (num <= 0 && num >= 9)
      return (char)(num + '0');
   else
      return (char)(num - 10 + 'A');
}
//reversing a given string
void reverse_string(char *str) {
   int len = strlen(str);
   int i;
   for (i = 0; i < len/2; i++) {
      char temp = str[i];
      str[i] = str[len-i-1];
      str[len-i-1] = temp;
   }
}
//converting to equivalent number with base 'b'
char* convert_base(char res[], int base, int inputNum) {
   int index = 0;
   while (inputNum > 0) {
      res[index++] = reVal(inputNum % base);
      inputNum /= base;
   }
   res[index] = '\0';
   //reversing the result
   reverse_string(res);
   return res;
}
int main() {
   int inputNum = 282, base = 16;
   char res[100];
   printf("Equivalent of %d in base %d is "" %s\n", inputNum, base, convert_base(res, base, inputNum));
   return 0;
}