Convert from any base to decimal and vice versa - GeeksforGeeks (2025)

// C++ program of the above approach#include <bits/stdc++.h>using namespace std;// To return char for a value. For example '2'// is returned for 2. 'A' is returned for 10. 'B'// for 11char reVal(int num){ if (num >= 0 && num <= 9) return (char)(num + '0'); else return (char)(num - 10 + 'A');}// Utility function to reverse a stringvoid strev(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; }}// Function to convert a given decimal number// to a base 'base' andchar* fromDeci(char res[], int base, int inputNum){ int index = 0; // Initialize index of result // Convert input number is given base by repeatedly // dividing it by base and taking remainder while (inputNum > 0) { res[index++] = reVal(inputNum % base); inputNum /= base; } res[index] = '\0'; // Reverse the result strev(res); return res;}// Driver Codeint main(){ int inputNum = 282, base = 16; char res[100]; cout << "Decimal Equivalent of " << fromDeci(res, base, inputNum) << " in base "<< base << " is " <<  inputNum; return 0;}// This code is contributed by code_hunt.

// C program to convert a number from any base// to decimal#include <stdio.h>#include <string.h>// To return value of a char. For example, 2 is// returned for '2'. 10 is returned for 'A', 11// for 'B'int val(char c){ if (c >= '0' && c <= '9') return (int)c - '0'; else return (int)c - 'A' + 10;}// Function to convert a number from given base 'b'// to decimalint toDeci(char *str, int base){ int len = strlen(str); int power = 1; // Initialize power of base int num = 0; // Initialize result int i; // Decimal equivalent is str[len-1]*1 + // str[len-2]*base + str[len-3]*(base^2) + ... for (i = len - 1; i >= 0; i--) { // A digit in input number must be // less than number's base if (val(str[i]) >= base) { printf("Invalid Number"); return -1; } num += val(str[i]) * power; power = power * base; } return num;}// Driver codeint main(){ char str[] = "11A"; int base = 16; printf("Decimal equivalent of %s in base %d is " " %d\n", str, base, toDeci(str, base)); return 0;}

// Java program to convert // a number from any base// to decimalimport java.io.*;class GFG {// To return value of a char. // For example, 2 is returned// for '2'. 10 is returned // for 'A', 11 for 'B'static int val(char c){ if (c >= '0' && c <= '9') return (int)c - '0'; else return (int)c - 'A' + 10;}// Function to convert a // number from given base // 'b' to decimalstatic int toDeci(String str,  int base){ int len = str.length(); int power = 1; // Initialize  // power of base int num = 0; // Initialize result int i; // Decimal equivalent is  // str[len-1]*1 + str[len-2] * // base + str[len-3]*(base^2) + ... for (i = len - 1; i >= 0; i--) { // A digit in input number  // must be less than  // number's base if (val(str.charAt(i)) >= base) { System.out.println("Invalid Number"); return -1; } num += val(str.charAt(i)) * power; power = power * base; } return num;}// Driver codepublic static void main (String[] args) { String str = "11A"; int base = 16; System.out.println("Decimal equivalent of "+  str + " in base "+ base +  " is "+ " "+  toDeci(str, base));}}// This code is contributed // by anuj_67.

# Python program to convert a # number from any base to decimal# To return value of a char. # For example, 2 is returned # for '2'. 10 is returned for 'A', # 11 for 'B' def val(c): if c >= '0' and c <= '9': return ord(c) - ord('0') else: return ord(c) - ord('A') + 10;# Function to convert a number # from given base 'b' to decimal def toDeci(str,base): llen = len(str) power = 1 #Initialize power of base num = 0 #Initialize result # Decimal equivalent is str[len-1]*1 +  # str[len-2]*base + str[len-3]*(base^2) + ...  for i in range(llen - 1, -1, -1): # A digit in input number must  # be less than number's base  if val(str[i]) >= base: print('Invalid Number') return -1 num += val(str[i]) * power power = power * base return num # Driver codestrr = "11A"base = 16print('Decimal equivalent of', strr, 'in base', base, 'is', toDeci(strr, base))# This code is contributed # by Sahil shelangia

// C# program to convert // a number from any base// to decimalusing System;class GFG {// To return value of a char. // For example, 2 is returned// for '2'. 10 is returned // for 'A', 11 for 'B'static int val(char c){ if (c >= '0' && c <= '9') return (int)c - '0'; else return (int)c - 'A' + 10;}// Function to convert a // number from given base // 'b' to decimalstatic int toDeci(string str,  int b_ase){ int len = str.Length; int power = 1; // Initialize  // power of base int num = 0; // Initialize result int i; // Decimal equivalent is  // str[len-1]*1 + str[len-2] * // base + str[len-3]*(base^2) + ... for (i = len - 1; i >= 0; i--) { // A digit in input number  // must be less than  // number's base if (val(str[i]) >= b_ase) { Console.WriteLine("Invalid Number"); return -1; } num += val(str[i]) * power; power = power * b_ase; } return num;}// Driver codepublic static void Main () { string str = "11A"; int b_ase = 16; Console.WriteLine("Decimal equivalent of "+  str + " in base "+ b_ase +  " is " + toDeci(str, b_ase));}}// This code is contributed // by anuj_67.

<script>// Javascript program to convert // a number from any base// to decimal// To return value of a char. // For example, 2 is returned// for '2'. 10 is returned // for 'A', 11 for 'B'function val(c){ if (c >= '0'.charCodeAt() &&  c <= '9'.charCodeAt()) return (c - '0'.charCodeAt()); else return (c - 'A'.charCodeAt() + 10);}// Function to convert a // number from given base // 'b' to decimalfunction toDeci(str, b_ase){ let len = str.length;  // Initialize  // power of base let power = 1;   // Initialize result let num = 0;  let i; // Decimal equivalent is  // str[len-1]*1 + str[len-2] * // base + str[len-3]*(base^2) + ... for(i = len - 1; i >= 0; i--) {  // A digit in input number  // must be less than  // number's base if (val(str[i].charCodeAt()) >= b_ase) { document.write("Invalid Number"); return -1; } num += val(str[i].charCodeAt()) * power; power = power * b_ase; } return num;}// Driver code let str = "11A";let b_ase = 16;document.write("Decimal equivalent of "+  str + " in base "+ b_ase +  " is " + toDeci(str, b_ase)); // This code is contributed by divyesh072019</script>

<?php// PHP program to convert a number from // any base to decimal// To return value of a char. For example,// 2 is returned for '2'. 10 is returned// for 'A', 11 for 'B'function val($c){ if ($c >= '0' && $c <= '9') return ord($c) - ord('0'); else return ord($c) - ord('A') + 10;}// Function to convert a number from given // base 'b' to decimalfunction toDeci($str, $base){ $len = strlen($str); $power = 1; // Initialize power of base $num = 0; // Initialize result // Decimal equivalent is str[len-1]*1 + // str[len-2]*base + str[len-3]*(base^2) + ... for ($i = $len - 1; $i >= 0; $i--) { // A digit in input number must be // less than number's base if (val($str[$i]) >= $base) { print("Invalid Number"); return -1; } $num += val($str[$i]) * $power; $power = $power * $base; } return $num;}// Driver code$str = "11A";$base = 16;print("Decimal equivalent of $str " . "in base $base is " . toDeci($str, $base));// This code is contributed by mits?>

// C++ Program to convert decimal to any given base#include <bits/stdc++.h>using namespace std;// To return char for a value. For example '2'// is returned for 2. 'A' is returned for 10. 'B'// for 11char reVal(int num){ if (num >= 0 && num <= 9) return (char)(num + '0'); else return (char)(num - 10 + 'A');}// Function to convert a given decimal number// to a base 'base' andstring fromDeci(string& res, int base, int inputNum){ int index = 0; // Initialize index of result // Convert input number is given base by repeatedly // dividing it by base and taking remainder while (inputNum > 0) { res.push_back(reVal(inputNum % base)); index++; inputNum /= base; } // Reverse the result reverse(res.begin(), res.end()); return res;}// Driver programint main(){ int inputNum = 282, base = 16; string res; cout << "Equivalent of " << inputNum << " in base " << base << " is " << fromDeci(res, base, inputNum) << endl; return 0;}// The code is contributed by Gautam goel (gautamgoel962)

// C Program to convert decimal to any given base#include <stdio.h>#include <string.h>// To return char for a value. For example '2'// is returned for 2. 'A' is returned for 10. 'B'// for 11char reVal(int num){ if (num >= 0 && num <= 9) return (char)(num + '0'); else return (char)(num - 10 + 'A');}// Utility function to reverse a stringvoid strev(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; }}// Function to convert a given decimal number// to a base 'base' andchar* fromDeci(char res[], int base, int inputNum){ int index = 0; // Initialize index of result // Convert input number is given base by repeatedly // dividing it by base and taking remainder while (inputNum > 0) { res[index++] = reVal(inputNum % base); inputNum /= base; } res[index] = '\0'; // Reverse the result strev(res); return res;}// Driver programint main(){ int inputNum = 282, base = 16; char res[100]; printf("Equivalent of %d in base %d is " " %s\n", inputNum, base, fromDeci(res, base, inputNum)); return 0;}

// Java Program to convert decimal to any given baseimport java.lang.*; import java.io.*; import java.util.*; class GFG{ // To return char for a value. For // example '2' is returned for 2. // 'A' is returned for 10. 'B' for 11static char reVal(int num){ if (num >= 0 && num <= 9) return (char)(num + 48); else return (char)(num - 10 + 65);}// Function to convert a given decimal number// to a base 'base' andstatic String fromDeci(int base1, int inputNum){ String s = ""; // Convert input number is given  // base by repeatedly dividing it // by base and taking remainder while (inputNum > 0) { s += reVal(inputNum % base1); inputNum /= base1; } StringBuilder ix = new StringBuilder();  // append a string into StringBuilder input1  ix.append(s);  // Reverse the result return new String(ix.reverse());}// Driver codepublic static void main (String[] args){ int inputNum = 282, base1 = 16; System.out.println("Equivalent of " + inputNum + " in base "+base1+" is " + fromDeci(base1, inputNum));}}// This code is contributed by mits

# Python3 Program to convert decimal to # any given base# To return char for a value. For example # '2' is returned for 2. 'A' is returned # for 10. 'B' for 11def reVal(num): if (num >= 0 and num <= 9): return chr(num + ord('0')); else: return chr(num - 10 + ord('A'));# Utility function to reverse a stringdef strev(str): len = len(str); for i in range(int(len / 2)): temp = str[i]; str[i] = str[len - i - 1]; str[len - i - 1] = temp;# Function to convert a given decimal # number to a base 'base' anddef fromDeci(res, base, inputNum): index = 0; # Initialize index of result # Convert input number is given base  # by repeatedly dividing it by base  # and taking remainder while (inputNum > 0): res+= reVal(inputNum % base); inputNum = int(inputNum / base); # Reverse the result res = res[::-1]; return res;# Driver CodeinputNum = 282;base = 16;res = "";print("Equivalent of", inputNum, "in base", base, "is", fromDeci(res, base, inputNum));# This code is contributed by mits 

// C# Program to convert decimal to any given baseusing System;using System.Collections;class GFG{ // To return char for a value. For // example '2' is returned for 2. // 'A' is returned for 10. 'B' for 11static char reVal(int num){ if (num >= 0 && num <= 9) return (char)(num + 48); else return (char)(num - 10 + 65);}// Function to convert a given decimal number// to a base 'base' andstatic string fromDeci(int base1, int inputNum){ string s = ""; // Convert input number is given  // base by repeatedly dividing it // by base and taking remainder while (inputNum > 0) { s += reVal(inputNum % base1); inputNum /= base1; } char[] res = s.ToCharArray(); // Reverse the result Array.Reverse(res); return new String(res);}// Driver codestatic void Main(){ int inputNum = 282, base1 = 16; Console.WriteLine("Equivalent of " + inputNum + " in base "+base1+" is " + fromDeci(base1, inputNum));}}// This code is contributed by mits

<script> // Javascript Program to convert decimal to any given base  // To return char for a value. For // example '2' is returned for 2. // 'A' is returned for 10. 'B' for 11 function reVal(num) { if (num >= 0 && num <= 9) return String.fromCharCode(num + 48); else return String.fromCharCode(num - 10 + 65); } // Function to convert a given decimal number // to a base 'base' and function fromDeci(base1, inputNum) { let s = ""; // Convert input number is given // base by repeatedly dividing it // by base and taking remainder while (inputNum > 0) { s += reVal(inputNum % base1); inputNum = parseInt(inputNum / base1, 10); } let res = s.split(''); // Reverse the result res.reverse(); return res.join(""); }  let inputNum = 282, base1 = 16; document.write("Equivalent of " + inputNum + " in base "+base1+" is " + fromDeci(base1, inputNum));// This code is contributed by rameshtravel07.</script>

<?php// PHP Program to convert decimal to // any given base// To return char for a value. For example '2'// is returned for 2. 'A' is returned for 10. // 'B' for 11function reVal($num){ if ($num >= 0 && $num <= 9) return chr($num + ord('0')); else return chr($num - 10 + ord('A'));}// Utility function to reverse a stringfunction strev($str){ $len = strlen($str); for ($i = 0; $i < $len / 2; $i++) { $temp = $str[$i]; $str[$i] = $str[$len - $i - 1]; $str[$len - $i - 1] = $temp; }}// Function to convert a given decimal // number to a base 'base' andfunction fromDeci($res, $base, $inputNum){ $index = 0; // Initialize index of result // Convert input number is given base  // by repeatedly dividing it by base  // and taking remainder while ($inputNum > 0) { $res.= reVal($inputNum % $base); $inputNum = (int)($inputNum / $base); } // Reverse the result $res = strrev($res); return $res;}// Driver Code$inputNum = 282;$base = 16;$res = "";print("Equivalent of $inputNum in base $base is " . fromDeci($res, $base, $inputNum));// This code is contributed by mits ?>

#include <iostream>#include <string>using namespace std;int main() { string n = "1100"; int b = 2; int result = stoi(n, nullptr, b); cout << result << endl; return 0;}

public class GFG { public static void main(String[] args) { String n = "1100"; int b = 2; int result = Integer.parseInt(n, b); System.out.println(result); }}

n = "1100"b = 2print(int(n, b))

using System;class Program { static void Main(string[] args) { string n = "1100"; int b = 2; int result = Convert.ToInt32(n, b); Console.WriteLine(result); }}

const n = '1100';const b = 2;const result = parseInt(n, b);console.log(result); // Output: 12