BUILT IN FUNCTIONS FOR STRING HANDLING
string.h
You may want to look at the section on arrays first!. The following macros are built into the file string.h

strcat Appends a string
strchr Finds first occurrence of a given character
strcmp Compares two strings
strcmpi Compares two strings, non-case sensitive
strcpy Copies one string to another
strlen Finds length of a string
strlwr Converts a string to lowercase
strncat Appends n characters of string
strncmp Compares n characters of two strings
strncpy Copies n characters of one string to another
strnset Sets n characters of string to a given character
strrchr Finds last occurrence of given character in string
strrev Reverses string
strset Sets all characters of string to a given character
strspn Finds first substring from given character set in string
strupr Converts string to uppercase

To convert a string to uppercase

#include <stdio.h>
#include <string.h>

main()
{
char name[80]; /* declare an array of characters 0-79 */

printf("Enter in a name in lowercase\n");
scanf( "%s", name );
strupr( name );
printf("The name is uppercase is %s", name );
}

Sample Program Output
Enter in a name in lowercase
samuel
The name in uppercase is SAMUEL

BUILT IN FUNCTIONS FOR CHARACTER HANDLING
The following character handling functions are defined in ctype.h

isalnum Tests for alphanumeric character
isalpha Tests for alphabetic character
isascii Tests for ASCII character
iscntrl Tests for control character
isdigit Tests for 0 to 9
isgraph Tests for printable character
islower Tests for lowercase
isprint Tests for printable character
ispunct Tests for punctuation character
isspace Tests for space character
isupper Tests for uppercase character
isxdigit Tests for hexadecimal
toascii Converts character to ascii code
tolower Converts character to lowercase
toupper Converts character to uppercase

To convert a string array to uppercase a character at a time using toupper()

#include <stdio.h>
#include <ctype.h>
main()
{
char name[80];
int loop;

printf("Enter in a name in lowercase\n");
scanf( "%s", name );
for( loop = 0; name[loop] != 0; loop++ )
name[loop] = toupper( name[loop] );

printf("The name is uppercase is %s", name );
}

Sample Program Output
Enter in a name in lowercase
samuel
The name in uppercase is SAMUEL