C++ Program For char to int Conversion

In C++, a character representing a decimal digit can be converted to its corresponding integer value using the character's position relative to '0'.

• For example, '9' can be converted to the integer 9 by subtracting '0'.
• For multi-digit values such as "123", use string-to-integer conversion methods such as stoi().

Examples:

Input: ch = '9'
Output: 9

Input: ch = '5'
Output: 5

Approaches to Convert char to int

The following approaches can be used:

1. Using ASCII Character Conversion

The characters '0' to '9' have consecutive character codes. Therefore, subtracting '0' from a digit character gives its corresponding integer value.

For example:

'9' - '0' = 9

#include <iostream>
using namespace std;

int main()
{
    char ch = '9';

    // Convert digit character to integer
    int num = ch - '0';

    cout << num;

    return 0;
}

9

Explanation

• The character '9' is subtracted from '0'.
• Since digit characters are stored consecutively, the result is the integer 9.

2. Using stoi()

The stoi() function can also be used by first converting the character into a one-character string.

#include <iostream>
#include <string>
using namespace std;

int main()
{
    char ch = '9';

    // Convert char to a one-character string
    string str(1, ch);

    // Convert string to integer
    int num = stoi(str);

    cout << num;

    return 0;
}

9

Explanation

• The character '9' is first converted into the string "9".
• stoi() then converts the string into the integer 9.

Important Points

• The ch - '0' approach is valid only for digit characters ('0' to '9'); it should not be used for arbitrary characters such as 'A'.
• atoi() expects a null-terminated C-style string, so it should not be used directly with a single char; for multi-digit strings such as "1234", use stoi().