C语言if语句 getchar putchar

// cypher1.c -- alters input, preserving spaces
#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;
}