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題目描述

? 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.
  

解題思路

首先，編寫一個小程序，獲得解嗎規則。

    #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;
}
  

解碼規則是ASCII碼值減7。

代碼實現

    #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