18. Hexadecimal Number Output | Basic I/O

📝 Problem

Get a value and print its corresponding hexadecimal number.

Input Format:
Accept an integer as a input

Output Format:
Display the output in hexadecimal format

Constraints:
1 <= inp< =10^16

🔢 Complete Guide to Number Base Formatting in C++

Understanding Number Bases

Computers can display the same number in different bases (number systems). C++ provides powerful manipulators to control how integers are displayed.

1️⃣ Number Base Manipulators

Manipulator	Base	Digits Used	Example (255)
`std::dec`	10 (Decimal)	0-9	`255`
`std::hex`	16 (Hexadecimal)	0-9, a-f	`ff`
`std::oct`	8 (Octal)	0-7	`377`

Basic Example:

int num = 255;
cout << dec << num << endl; // 255
cout << hex << num << endl; // ff
cout << oct << num << endl; // 377

⚠️ Important: Stateful Behavior

Base manipulators are persistent — once set, they affect all future outputs until changed. Always reset if needed!

2️⃣ Hexadecimal Letter Case

std::uppercase → prints hex letters A–F in uppercase
std::nouppercase → prints letters a–f (default)

Case Example:

int num = 255;
cout << hex << num << endl;                      // ff
cout << uppercase << hex << num << endl;      // FF

3️⃣ Showing Base Prefix

std::showbase → adds prefix (0x for hex, 0 for octal)
std::noshowbase → disables prefix (default)

Prefix Examples:

int num = 255;
cout << showbase << hex << num << endl;               // 0xff
cout << uppercase << hex << num << endl;      // 0XFF
cout << oct << num << endl;                      // 0377

4️⃣ Field Width & Padding

Manipulator	Purpose	Duration
`setw(n)`	Set width to n characters	Next output only
`setfill(c)`	Fill character for padding	Persistent

Width & Padding:

int num = 255;
cout << setw(6) << setfill('0') << hex << num;
// Output: 0000ff

5️⃣ Handling Negative Numbers

Negative numbers show a minus sign in hex/octal by default:

Negative Numbers:

int n = -255;
cout << hex << n;  // -ff

// Two's complement (unsigned style):
cout << hex << static_cast<unsigned int>(n);
// Output: ffffff01

6️⃣ Complete Example - All Together

int num;
cin >> num;

// Decimal
cout << "Decimal: " << dec << num << '\n';

// Hex lowercase
cout << "Hex: " << hex << nouppercase << num << '\n';

// Hex uppercase with 0x prefix
cout << "Hex (0X): " << showbase << uppercase << num << '\n';

// Octal with prefix
cout << "Octal: " << showbase << oct << num << '\n';

// Padded hex
cout << setw(6) << setfill('0') << hex << num;

// Reset to default
cout << dec << noshowbase << nouppercase;

✅ Key Tips Beginners Often Miss

                            Hex stays active until changed → always reset if needed
showbase + uppercase = 0XFF (not just FF)
setw() only affects next value, setfill() sticks
Negative numbers behave differently with signed vs unsigned cast
Hex manipulators don't work for floats (unless hexfloat is used)

                        

📊 Quick Reference

Goal	Code
Lowercase hex	`hex << nouppercase`
Uppercase hex	`hex << uppercase`
Hex with 0x	`showbase << hex`
Padded hex	`setw(n) << setfill('0') << hex`
Reset to decimal	`dec << noshowbase`

Examples

Sample Input 1:

Input:

100

Sample Output 1:

Output:

Explanation: 100 in decimal = 64 in hexadecimal (6×16 + 4 = 100)

Sample Input 2:

Input:

10245

Sample Output 2:

Output:

2805

Explanation: 10245₁₀ = 2805₁₆ (2×16³ + 8×16² + 0×16 + 5 = 10245)

Solution.cpp

#include <iostream>
#include <iomanip>

using namespace std;

int main() {
    long long a;
    cin >> a;
    
    // hex: Displays number in hexadecimal (base 16)
    // Uses digits 0-9 and letters a-f
    // Example: 100 → 64, 255 → ff
    cout << hex << a;
    
    return 0;
}