C语言转换大小写

#include <stdio.h>
#include <ctype.h>  // Contains the tolower prototype
void main (void)
{
    int letter;
    for (letter = getchar(); ! feof(stdin); letter = getchar())
        putchar(tolower(letter));
} 

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

void main (void)
{
    char line[];  // Line of text read
    while (fgets(line, sizeof(line), stdin))
        fputs(strupr(line), stdout);
}  

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