🧠 Convert Lowercase to Uppercase in C Without strupr()

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🔠 Convert Lowercase to Uppercase in C Manually (Without strupr())

This tutorial demonstrates how to convert all lowercase letters in a string to uppercase manually using ASCII values, without relying on the built-in strupr() function.

We'll provide two methods:

• ✅ Using a custom function
• 🛠️ Without using a function (logic in main())

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✅ Method 1: Using a Custom Function

#include <stdio.h>

void toUpperCase(char str[]) {
    for (int i = 0; str[i] != '\0'; i++) {
        // Check if lowercase letter
        if (str[i] >= 'a' && str[i] <= 'z') {
            // Convert to uppercase by subtracting 32
            str[i] = str[i] - 32;
        }
    }
}

int main() {
    char str[100];

    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);

    toUpperCase(str);

    printf("Uppercase string: %s", str);

    return 0;
}

🧠 Explanation:

• ASCII value for 'a' to 'z' is 97 to 122.
• ASCII value for 'A' to 'Z' is 65 to 90.
• Subtracting 32 converts a lowercase letter to uppercase.

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🛠️ Method 2: Without Function (All Logic Inside main())

#include <stdio.h>

int main() {
    char str[100];

    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);

    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] >= 'a' && str[i] <= 'z') {
            str[i] = str[i] - 32;
        }
    }

    printf("Uppercase string: %s", str);

    return 0;
}

📌 Summary

Manual conversion of lowercase letters to uppercase helps you understand ASCII codes and character manipulation in C.

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