大小写字符的转换。然后输出ASCII码，怎么做，求大佬告知！

#include <stdio.h>
#define N 10
int main( ) {
int i;
char a[10] = "ABC def !";
printf( "%s\n", a );
//打印字符和ACSII编码
for ( i = 0; i < N; i++ )
printf( "%4c", a[i] );
printf( "\n" );
for ( i = 0; i < N; i++ )
printf( "%4d", a[i] );
printf( "\n\n" );
i = 0;
while ( a[i] ) {
if ( 'A' <= a[i] && a[i] <= 'Z' )
a[i] = a[i] - 'A' + 'a';
else if ( 'a' <= a[i] && a[i] <= 'z' )
a[i] = a[i] - 'a' + 'A';
i++;
}
printf( "%s\n", a );
//打印字符和ACSII编码
for ( i = 0; i < N; i++ )
printf( "%4c", a[i] );
printf( "\n" );
for ( i = 0; i < N; i++ )
printf( "%4d", a[i] );
printf( "\n" );
}