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Basic
Switch Case
Goto
Operators
if Statement
Nested if
While Loop
For Loop
Patterns
Array
2D Array
String Function Example
Pointers
Recursion Function
Structure
Excersises
Others



C Program to Convert a String to Uppercase and Lowercase


Write a C program to convert a string to uppercase and lowercase.

  • Reads a string from input one character at a time until newline (\n) is encountered.
  • Stores the null terminator (\0) to properly mark the end of the string.
  • Converts and prints each lowercase letter to uppercase by subtracting 32 from its ASCII value.
  • Converts and prints each uppercase letter to lowercase by adding 32 to its ASCII value.
Example : pgm.c 
#include <stdio.h>

int main() {
    char str[100];
    int i = 0;

    printf("Enter a string: ");
    while ((str[i] = getchar()) != '\n') {
        i++;
    }
    str[i] = '\0';

    // Convert to Uppercase
    printf("Uppercase: ");
    for (i = 0; str[i] != '\0'; i++) {
        if (str[i] >= 'a' && str[i] <= 'z') {
            printf("%c", str[i] - 32);  // 'a' to 'A' = ASCII -32
        } else {
            printf("%c", str[i]);
        }
    }

    // Convert to Lowercase
    printf("\nLowercase: ");
    for (i = 0; str[i] != '\0'; i++) {
        if (str[i] >= 'A' && str[i] <= 'Z') {
            printf("%c", str[i] + 32);  // 'A' to 'a' = ASCII +32
        } else {
            printf("%c", str[i]);
        }
    }

    printf("\n");
    return 0;
}

Output :

Enter a string: Hello World
Uppercase: HELLO WORLD
Lowercase: hello world