Question

Create a C program:

A caesar cipher is a simple cipher that shifts letters in a string. For example, shifting “ab” over by 1 would result in “bc”, and shifting “xyz” over by 2 would result in “zab”. The caesar program should take, in the command line an integer k, the amount to shift some text by, and a string f i l e, the name of a file containing text to encode using the cipher.

For example, suppose “secret.txt” contains “defend the east wall of the castle”, then running caesar with 3 should result in the following:

$ cat secret.txt

defend the east wall of the castle

$ ./caesar 3 secret.txt

ghihqg wkh hdvw zdoo ri wkh fdvwoh

Answer 1

Hi... Please chekc the below c code.

Main.c

#include<stdio.h>
#include<string.h>
int main(int argc,char* argv[])
{
int counter;
int val = 0;
//printf("Program Name Is: %s",argv[0]);
if(argc==1)
printf("\nNo Extra Command Line Argument Passed Other Than Program Name");
if(argc>=2)
{
val = atoi(argv[1]);
//printf("\n%s: %s",argv[1],argv[2]);

char c[1000];
FILE *fptr;

if ((fptr = fopen(argv[2], "r")) == NULL)
{
printf("Error! opening file");
// Program exits if file pointer returns NULL.
exit(1);
}

// reads text until newline
fscanf(fptr,"%[^\n]", c);

printf("Data from the file:\n%s", c);
fclose(fptr);
  
char new[strlen(c)];
int index = 0;
char smallalphabet[26] = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
for(int i=0;i<strlen(c);i++){
bool flag = false;
for(int k=0;k<26;k++){
  
if(c[i]==smallalphabet[k]){
index = k+val;
if(index>25){
index = index - 26;
}
new[i] = smallalphabet[index];
//printf("matched\n");
flag = true;
break;
}
  
}
if(!flag){
new[i] = c[i];
}
  
}
  
printf("\nOutput file:\n%s", new);
}
return 0;
}

Input:

example.txt

abcd

Output: --- /Main.c 3 example.txt

Data from the file:                                                                                                   

abcd                                                                                                                  

Output file:                                                                                                   

defg

Please text the code and let me know querries. Thank you. All the best.