C++ char to int Conversion

Converting a char to an int in C++ sounds simple, but it trips up almost every beginner — because a char is already a number under the hood. What you do next depends on whether you want the digit it shows or the ASCII code behind it. Let’s clear it up.

The Trap: a char Already Holds a Number

Every char stores a small integer called its ASCII code. So “converting” isn’t really about changing types — it’s about deciding which number you want:

#include <iostream>

int main() {
    char c = '7';
    std::cout << c << "\n";        // prints 7  (the character)
    std::cout << (int)c << "\n";   // prints 55 (its ASCII code)
    return 0;
}

The character '7' has the ASCII code 55. If you cast it straight to int, you get 55, not 7. That surprise is the root of almost every char-to-int bug.

Convert a Digit Character to Its Value

When you have a single digit like '7' and want the number 7, subtract the character '0':

#include <iostream>

int main() {
    char digit = '7';
    int value = digit - '0';        // 55 - 48 = 7
    std::cout << value * 2 << "\n"; // 14 — real arithmetic now
    return 0;
}

This works because the digit characters '0' through '9' sit in consecutive order in ASCII. '0' is 48, so subtracting it shifts any digit down to its true value. It’s the single most useful char trick in C++.

Get the ASCII Code on Purpose

Sometimes you do want the ASCII code — for example, to check ranges or do character math. Make that intent obvious with static_cast<int>:

#include <iostream>

int main() {
    char letter = 'A';
    int code = static_cast<int>(letter);  // 65
    std::cout << letter << " has ASCII code " << code << "\n";
    return 0;
}

static_cast<int> is the modern, readable way to say “I really do mean the numeric code.” It’s clearer than the old C-style (int)letter and easier to spot when reading code later.

Convert a Whole Number String

If your characters form a multi-digit number stored in a std::string, don’t loop digit by digit — use std::stoi (“string to int”):

#include <iostream>
#include <string>

int main() {
    std::string text = "452";
    int number = std::stoi(text);   // 452
    std::cout << number + 1 << "\n"; // 453
    return 0;
}

std::stoi parses the whole string at once and even handles a leading minus sign. Reach for it whenever you’re turning user input or file text into a number.

Going the Other Way: int to char

To turn a single-digit number back into its character, add '0':

#include <iostream>

int main() {
    int n = 5;
    char digit = n + '0';          // '5'
    std::cout << digit << "\n";    // 5 (as a character)
    return 0;
}

Adding '0' is the mirror image of subtracting it. This pairs nicely with building strings character by character.

Quick Reference

Related Articles

• How to Convert String to int in C++ — stoi, atoi, and stringstream
• C++ int to string Conversion — every method explained
• C++ Type Casting Explained — static_cast and friends
• C++ String vs char array — when to use each
• C++ Variables and Data Types — how char really works

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