Signed and Unsigned Char Type

Introduction

In the previous tutorial, we learned about the close relationship between the integer and character data types. It’s not surprising that the char type can be either signed or unsigned. In most cases, when we use the char type to store characters, it doesn’t matter whether it’s signed or unsigned. However, it becomes important to know the difference between signed and unsigned char types when we use them to store small integers.

In most computer systems, the char type is 1 byte long, making it suitable for storing small integers. Typically, the int type is 2 bytes long, but when we need to store very small integers, some programmers prefer to use char type variables to save memory. Similar to the int type, the char type can be signed or unsigned. Now, let’s explore the difference between these two categories.

Signed Characters

In some textbooks, it is mentioned that by default, the char type is signed. However, it’s important to note that the original C standard does not specify whether the char type is signed or unsigned. Assuming that the char type is signed is not recommended because it can lead to unexpected results, especially when using char to store integers and performing basic calculations on them.

Signed characters have the ability to represent both negative and positive values. The typical range of values for a signed character is -128 to 127. In this range, 7 bits are used to represent the magnitude of the number, while the Most Significant Bit (MSB) is reserved for the sign bit, indicating whether the value is negative or positive.

However, it’s important to emphasize that most of the time, especially when using the char type to store characters, it doesn’t matter whether the char type is signed or unsigned. The existence of the signed char type is primarily for the purpose of easily representing small integers, both negative and positive. Therefore, when dealing with characters, it is generally not necessary to specify whether a char is signed or unsigned.

Unsigned Characters

If required, the char type can be declared as unsigned by using the keyword “unsigned” before the char type. When a char is declared as unsigned, it can only represent positive values or zero. The range of values for an unsigned character is typically from 0 to 255. This range is possible because the char type occupies 1 byte of memory.

Declaring a char as unsigned allows all the bits of the char to be used for representing the magnitude of the value, without reserving a bit for the sign. This means that all 8 bits of the char are utilized to represent positive values, enabling a wider range of numbers to be stored compared to signed characters.

By declaring a char as unsigned, you ensure that it can only hold non-negative values, which can be useful in scenarios where you want to restrict the char to positive values or need to perform bitwise operations that rely on the full range of values.

Overall, specifying the char type as unsigned provides a wider range of positive values that can be stored within a char variable, making it suitable for situations where you don’t need to represent negative numbers.

The Program

Let’s consider a simple program to demonstrate the use of signed and unsigned char types for storing small integers:

#include <stdio.h>

int main() {
    char signedChar = -10;
    unsigned char unsignedChar = 255;

    printf("Signed Character: %d\n", signedChar);
    printf("Unsigned Character: %d\n", unsignedChar);

    signedChar = signedChar + 139;  
    unsignedChar = unsignedChar + 1;

    printf("Signed Character: %d\n", signedChar);
    printf("Unsigned Character: %d\n", unsignedChar);

    return 0;
}

Output:

In the given program, we have two variables: signedChar of type signed char and unsignedChar of type unsigned char. signedChar is initialized with a value of -10, and unsignedChar is initialized with a value of 255.

We then print the initial values of both variables. The output will display -10 for the signed character and 255 for the unsigned character.

Next, we perform arithmetic operations on these variables. We add 139 to signedChar and 1 to unsignedChar.

After the additions, the value of signedChar becomes -127. This is because adding 139 to -10 results in 129, which exceeds the range of signed characters (-128 to 127). When a value exceeds this range, it wraps around to the opposite end. In this case, 129 wraps around to -127 within the valid range.

Similarly, for unsignedChar, the value becomes 0. Adding 1 to 255 results in 256, which is greater than the maximum value in the range of unsigned characters (0 to 255). As a result, the value wraps around to 0.

Thus, the output of the program will display -127 for the signed character and 0 for the unsigned character.

This demonstrates the behavior of wrapping around when values exceed the range of their respective character types.

Summary

This tutorial explains the classification of the char type into signed and unsigned categories and highlights the importance of understanding this distinction. It emphasizes that while the signedness of char doesn’t matter when storing characters, it becomes significant when using char to store small integers. The tutorial provides an overview of signed and unsigned characters, their respective value ranges, and the wrap-around behavior when values exceed these ranges. A simple program is included to demonstrate the usage of signed and unsigned char types. Understanding the difference between signed and unsigned char is crucial for correctly representing and manipulating small integer values.