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题目描述

The Decoder

Write a complete program that will correctly decode a set of characters into a valid message. Your program should read a given file of a simple coded set of characters and print the exact message that the characters contain. The code key for this simple coding is a one for one character substitution based upon a  single arithmetic manipulation  of the printable portion of the ASCII character set.

Input and Output

For example: with the input file that contains:

    1JKJ'pz'{ol'{yhklthyr'vm'{ol'Jvu{yvs'Kh{h'Jvywvyh{pvu5
1PIT'pz'h'{yhklthyr'vm'{ol'Pu{lyuh{pvuhs'I|zpulzz'Thjopul'Jvywvyh{pvu5
1KLJ'pz'{ol'{yhklthyr'vm'{ol'Kpnp{hs'Lx|pwtlu{'Jvywvyh{pvu5
  

your program should print the message:

    *CDC is the trademark of the Control Data Corporation.
*IBM is a trademark of the International Business Machine Corporation.
*DEC is the trademark of the Digital Equipment Corporation.
  

Your program should accept all sets of characters that use the same encoding scheme and should print the actual message of each set of characters.

Sample Input

    1JKJ'pz'{ol'{yhklthyr'vm'{ol'Jvu{yvs'Kh{h'Jvywvyh{pvu5
1PIT'pz'h'{yhklthyr'vm'{ol'Pu{lyuh{pvuhs'I|zpulzz'Thjopul'Jvywvyh{pvu5
1KLJ'pz'{ol'{yhklthyr'vm'{ol'Kpnp{hs'Lx|pwtlu{'Jvywvyh{pvu5
  

Sample Output

    *CDC is the trademark of the Control Data Corporation.
*IBM is a trademark of the International Business Machine Corporation.
*DEC is the trademark of the Digital Equipment Corporation.
  

解题思路

首先，编写一个小程序，获得解吗规则。

    #include <stdio.h>
int main(void) {
	char s1[] = "1JKJ'pz'{ol'{yhklthyr'vm'{ol'Jvu{yvs'Kh{h'Jvywvyh{pvu5";
	char s2[] = "*CDC is the trademark of the Control Data Corporation.";
	int i = 0;
	while(s1[i] != '\0') {
		printf("%4d%4d\n", s1[i], s2[i]);
		i++;
	}
	return 0;
}
  

解码规则是ASCII码值减7。

代码实现

    #include <stdio.h>
int main(void) {
	int c;
	while((c = getchar()) != EOF) {
		if(c == '\n') {
			putchar('\n');
		} else {
			putchar(c - 7);
		}
	}
	return 0;
}
  

（全文完）

The Decoder - UVa458