Because why the hell not

overkill.c

#include <stdio.h> // getchar
#include <stdbool.h> // bool, true/false
#include <stdlib.h> // Malloc

typedef ptrdiff_t intz;
typedef size_t intuz;

typedef struct string_ {
	char* data;
	intz len;
} string;

// This is just sugar syntax for a pointer
// Copies an existing string pointer, rather than referencing it
string string_create( char str[] ) {
	string s;
	s.data = 0;
	s.len = 0;
	if ( str == 0 ) {
		// Ensure there is always a string,
		// just that it's the empty c-style string ""
		s.data = malloc( 1 );
		s.len = 0;
		s.data[ 0 ] = '\0';
		return s;
	}
	char* strbegin = str;
	while ( str[0] != '\0' ) {
		++s.len;
		++str;
	}
	s.data = malloc( s.len + 1 );
	str = strbegin;
	for ( intz i = 0; i < s.len; ++i ) {
		s.data[ i ] = str[ i ];
	}
	// Always null terminate
	s.data[ s.len ] = '\0';
	return s;
}

string string_copy( string copy ) {
	string s;
	if ( copy.data == 0 || copy.len == 0 ) {
		// Zero copy (empty string always)
		s.data = malloc( 1 );
		s.data[ 0 ] = '\0';
		s.len = 0;
	}
	s.data = malloc( copy.len + 1 );
	s.len = copy.len;
	for ( intz i = 0; i < copy.len; ++i ) {
		s.data[ i ] = copy.data[ i ];
	}
	// Always null terminate
	s.data[ s.len ] = '\0';
	return s;
}

string string_free( string s ) {
	free( s.data );
	s.data = 0;
	// We don't really need to do this
	// Since we're using "value semantics" (not really)
	// But why not?
	s.len = 0;
	return s;
}

void string_uppercase( string s ) {
	// Not unicode safe... but we're only doing ASCII! :D
	for ( intz i = 0; i < s.len; ++i ) {
		char c = s.data[ i ];
		if ( c >= 'a' && c <= 'z' ) {
			s.data[ i ] -= 32;
		}
	}
}

string get_line( ) {
	char buffer[ 1024 ] = { 0 };
	char* bufferptr = buffer;
	while ( true ) {
		int c = getchar( );
		if ( c == EOF || c == '\n' ) {
			bufferptr[ 0 ] = '\0';
			break;
		}
		bufferptr[ 0 ] = c;
		++bufferptr;
		if ( bufferptr == &buffer[ 1024 ] ) {
			// TODO: line is longer than 1024 characters
			// panic or build a bigger string or something
		}
	}
	return string_create( buffer );
}

int main( ) {

	// Get the line
	string s = get_line();
	// Copy the string to have something to work with
	// Potential to do: print lowercase, uppercase it, print uppercase.
	// Saves on copy
	string su = string_copy( s );
	// Uppercase it
	string_uppercase( su );
	
	// Print the value
	printf( "Lowercase string: %s\nUppercase string: %s", s.data, su.data );
	
	// Proper cleanup since there's no expections or RAII
	s = string_free( s );
	su = string_free( su );
}