Convert String into Upper Case in C – Simple Program for Beginners

Introduction

In this post, you’ll learn how to convert a string into upper case using C programming. Converting strings to upper case is a common task in text processing, useful in formatting, comparisons, and standardizing inputs.

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C Program to Convert String into Upper Case

#include <stdio.h>
#include <ctype.h>

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

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

    for (i = 0; str[i] != '\0'; i++) {
        str[i] = toupper(str[i]);
    }

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

    return 0;
}

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Explanation

• fgets() is used to read the input string, including spaces.
• The toupper() function from ctype.h is used to convert each character to upper case.
• A loop processes each character of the string and updates it in place.

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Sample Output

Enter a string: hello world
Uppercase string: HELLO WORLD

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Use Cases

• Standardizing user inputs (e.g., usernames or email addresses).
• Case-insensitive string comparisons.
• Preprocessing text for search or filtering.