What is the method for converting the size of a charact…

You can use the standard library functions toupper() and tolower() in the C language ctype.h header file to convert the case of a character array.

The toupper() function converts a character to its uppercase form, and returns the original character if it is not a lowercase letter.

The tolower() function converts a character to lowercase. If the character is not an uppercase letter, the original character is returned.

Here is an example code using the toupper() and tolower() functions for case conversion:

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

void toUpperCase(char str[]) {
    int i = 0;
    while (str[i] != '\0') {
        str[i] = toupper(str[i]);
        i++;
    }
}

void toLowerCase(char str[]) {
    int i = 0;
    while (str[i] != '\0') {
        str[i] = tolower(str[i]);
        i++;
    }
}

int main() {
    char str[] = "Hello World";

    toUpperCase(str);
    printf("Uppercase: %s\n", str);

    toLowerCase(str);
    printf("Lowercase: %s\n", str);

    return 0;
}

Output result:

Uppercase: HELLO WORLD
Lowercase: hello world

In the example above, the toUpperCase() function converts all characters in a string to uppercase, while the toLowerCase() function converts all characters to lowercase.