Solution of 458 - The Decoder

Problem Description
source: https://uva.onlinejudge.org/external/4/458.html

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.

Solution:

#include<stdio.h>
#define max 100000

int main()
{
    long int i;
    char str[max];
    while(gets(str))
    {
        for(i=0;str[i]!='\0';i++)
        {
            printf("%c",str[i]-7);
        }
        printf("\n");
    }
    return 0;
}