C - Character Arithmetic

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In C, character arithmetic means performing arithmetic operations like addition, subtraction, multiplication, and division on characters. Characters in C are stored as numbers using the ASCII system.

The ASCII system represents each character, digit, or symbol using numbers. For example, 'A' is stored as 65, 'B' as 66, 'a' as 97, and so on

Character Arithmetic Operations

To perform arithmetic operations on a character, we should know that a character takes 1 byte of memory. A signed char has a range from -128 to 127, and an unsigned char has a range from 0 to 255.

Checking Character Values

Let's first see a character and its ASCII value. In the below example, we print the character 'A' using %c and its ASCII value using %d.

#include <stdio.h>
int main() {
    char ch = 'A';
    printf("Character: %c\n", ch);
    printf("ASCII Value: %d\n", ch);
    return 0;
}

After running the program, we can see the character and its ASCII value-

Character: A
ASCII Value: 65

Adding Two Characters

We can add characters just like numbers because each character is stored as a number.

#include <stdio.h>

int main() {
    char a = 'A';
    char b = 'B';

    printf("a = %c\n", a);
    printf("b = %c\n", b);
    printf("a + b = %c\n", a + b);
    printf("a + b (as number) = %d\n", a + b);
    return 0;
}

Here's the output of the above program after adding the characters -

a = A
b = B
a + b = â
a + b (as number) = 131

In this program, the characters a and b are declared and assigned with values 'A' and 'B'. When we add a and b, the result is the character â. The ASCII value of A is 65 and B is 66, so adding them gives 65 + 66 = 131. The character with ASCII value 131 is â.

Shifting and Subtracting Characters

We can shift a character forward or backward by adding or subtracting a number. For example, 'A' + 1 gives 'B' and 'C' - 1 gives 'B'. We can also find the difference between characters using subtraction, like 'C' - 'A', which gives 2 because the ASCII value of 'C' is 67 and 'A' is 65, so 67 - 65 = 2.

#include <stdio.h>

int main() {
    char c1 = 'A' + 1; 
    char c2 = 'C' - 1; 
    int diff = 'C' - 'A';

    printf("A + 1 = %c\n", c1);
    printf("C - 1 = %c\n", c2);
    printf("C - A = %d\n", diff);
    return 0;
}

Here's the output of the program after shifting and subtracting the characters -

A + 1 = B
C - 1 = B
C - A = 2

Comparing Two Characters

We can compare characters directly using comparison operators like <, >, <=, >=, ==, and != to check the order or equality of characters. In the program below, we check if the character 'a' comes before 'z'. Since the ASCII value of 'a' is 97 and 'z' is 122, so 'a' < 'z' is true.

#include <stdio.h>
int main() {
    if ('a' < 'z') {
        printf("'a' comes before 'z'\n");
    }
    return 0;
}

Here's the output that shows which character comes first.

'a' comes before 'z'

Increment and Decrement Operators on Characters

Characters in C can be incremented (++) or decremented (--) like numbers. Incrementing moves a character forward in the ASCII table, and decrementing moves it backward. In the below program, chracter ch starts as 'A'. After ch++, it becomes 'B', and after ch-- it becomes 'A' again.

#include <stdio.h>

int main() {
    char ch = 'A';
    printf("Original character: %c\n", ch);

    ch++; // Increment
    printf("After increment: %c\n", ch);

    ch--; // Decrement
    printf("After decrement: %c\n", ch);
    return 0;
}

Following is the output of the above program-

Original character: A
After increment: B
After decrement: A

Converting to Uppercase and Lowercase

In ASCII, the difference between uppercase and lowercase letters is 32. To convert an uppercase letter to lowercase, we add 32 to it. For example, 'M' + 32 becomes 'm'. Similarly, to convert a lowercase letter to uppercase, we subtract 32 from it. For example, 'm' - 32 becomes 'M'.

#include <stdio.h>

int main() {
    char upper = 'M';
    char lower = upper + 32; // Convert uppercase to lowercase
    
    char small = 'm';
    char capital = small - 32; // Convert lowercase to uppercase
    
    printf("Original Uppercase: %c\n", upper);
    printf("Converted to Lowercase: %c\n", lower);
    printf("Original Lowercase: %c\n", small);
    printf("Converted to Uppercase: %c\n", capital);
    return 0;
}

Here is the output of the above program that shows the original characters and their converted form.

Original Uppercase: M
Converted to Lowercase: m
Original Lowercase: m
Converted to Uppercase: M

In this chapter, we covered how to perform different types of arithmetic operations on characters in C. It is possible to perform such arithmetic operations on characters directly because the computer stores each character as a number, which allows us to add, subtract, compare and so on.