toupper() function in C

Last Updated : 10 Jan, 2025

The toupper() function is used to convert lowercase alphabet to uppercase. i.e. If the character passed is a lowercase alphabet then the toupper() function converts a lowercase alphabet to an uppercase alphabet. It is defined in the ctype.h header file.
Syntax:

int toupper(int ch);

Parameter: It accepts a single parameter:

ch: This represents the character to be converted to uppercase.

Returns: This function returns the uppercase character corresponding to the ch.

Below programs illustrate the toupper() function in C:
Example 1:-

// C program to demonstrate
// example of toupper() function.
#include <ctype.h>
#include <stdio.h>

int main()
{
    char ch;

    ch = 'g';
    printf("%c in uppercase is represented as  %c",
           ch, toupper(ch));

    return 0;
}

Output

g in uppercase is represented as  G

Example 2:-

// C program to demonstrate
// example of toupper() function.
#include <ctype.h>
#include <stdio.h>

int main()
{
    int j = 0;
    char str[] = "geekforgeeks\n";
    char ch;

    while (str[j]) {
        ch = str[j];
        putchar(toupper(ch));
        j++;
    }

    return 0;
}

Output

GEEKFORGEEKS

Note:

If the character passed in the toupper() is any of these three

1. uppercase character

2. special symbol

3. digit

toupper() will return the character as it is.

Example :

// C program to demonstrate
// example of toupper() function.
#include <ctype.h>
#include <stdio.h>

int main()
{
    int j = 0;
    char str[] = "GeEks@123\n";
    char ch;

    while (str[j]) {
        ch = str[j];
        putchar(toupper(ch));
        j++;
    }

    return 0;
}
// code is contributed by codersaty

Output:

GEEKS@123

toupper() function in C

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