求助关于这个循环先后的问题

因为标准输入是同步IO函数，运行时会阻塞，直到按下回车键时恢复执行。

#include <stdio.h>
#define SPACE ' ' // that's quote-space-quote
int main(void)
{
char ch;
ch = getchar(); // read a character
while (ch != '\n') // while not end of line
{
if (ch == SPACE) // leave the space
putchar(ch); // character unchanged
else
putchar(ch + 1); // change other characters
ch = getchar(); // get next character
}
putchar(ch);
// print the newline
return 0;
}