C Program to Convert a Char From Upper to Lower and Vice Versa in a Single Line Efficiently

Here we will build a program to showcase an efficient way to convert a char from upper to lower and vice versa in C in a single line. Below is one example which explains how bitwise operators help in efficient programming and also convert the given alphabet from one case to another.

Example:

C

// C program to demonstrate converting of
// char from upper to lower and vice-versa
// then printing it in a same line
#include <stdio.h>

// Flip the 5th position of the char using XOR operator
#define convert_case(c)    c^(1<<5)

// Set the 5th position of the char
#define to_lower(c)        c|(1<<5)

// clear the 5th position of the char
#define to_upper(c)        c&~(1<<5)

int main()
{
      char ch_u = 'S';
      char ch_l = 's';
      char ch = 's';

      printf("convert: %c, to_lower: %c, to_upper: %c\n",
     convert_case(ch), to_lower(ch_u), to_upper(ch_l));
    return 0;
}

Output

convert: S, to_lower: s, to_upper: S

Explanation:

• The difference between upper case and lower case in ASCII is 32 (‘A’ – ‘a’) 
• So, in the lower case of the alphabet character always 5th position is set (assuming little endian here)