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C Exercises: Encrypt a text file

C File Handling : Exercise-13 with Solution

Write a program in C to encrypt a text file.

 Assume that, the content of the file test.txt is  :                                                                       
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Sample Solution:

C Code:

#include <stdio.h>
#include <stdlib.h>

void main()
{
	char fname[20], ch;
	FILE *fpts, *fptt;
	
	printf("\n\n Encrypt a text file :\n");
	printf("--------------------------\n"); 	
	
	printf(" Input the name of file to encrypt : ");
	scanf("%s",fname);	

	fpts=fopen(fname, "r");
	if(fpts==NULL)
	{
		printf(" File does not exists or error in opening..!!");
		exit(1);
	}
	fptt=fopen("temp.txt", "w");
	if(fptt==NULL)
	{
		printf(" Error in creation of file temp.txt ..!!");
		fclose(fpts);
		exit(2);
	}
	while(1)
	{
		ch=fgetc(fpts);
		if(ch==EOF)
		{
			break;
		}
		else
		{
			ch=ch+100;
			fputc(ch, fptt);
		}
	}
	fclose(fpts);
	fclose(fptt);
	fpts=fopen(fname, "w");
	if(fpts==NULL)
	{
		printf(" File does not exists or error in opening..!!");
		exit(3);
	}
	fptt=fopen("temp.txt", "r");
	if(fptt==NULL)
	{
		printf(" File does not exists or error in opening..!!");
		fclose(fpts);
		exit(4);
	}
	while(1)
	{
		ch=fgetc(fptt);
		if(ch==EOF)
		{
			break;
		}
		else
		{
			fputc(ch, fpts);
		}
	}
	printf(" File %s successfully encrypted ..!!\n\n", fname);
	fclose(fpts);
	fclose(fptt);
}

Sample Output:

 Encrypt a text file :                                                                                        
--------------------------                                                                                    
 Input the name of file to encrypt : test.txt                                                                 
 File test.txt successfully encrypted ..!!

If you read the file test.txt you will see the following :

������Ʉ�ӄۗ�������ɒ��ђn

Flowchart:

Flowchart: Encrypt a text file

C Programming Code Editor:

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Previous: Write a program in C to merge two files and write it in a new file.
Next: Write a program in C to decrypt a previously encrypted file file.

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C Programming: Tips of the Day

Difference between signed / unsigned char :

There's no dedicated "character type" in C language. char is an integer type, same (in that regard) as int, short and other integer types. char just happens to be the smallest integer type. So, just like any other integer type, it can be signed or unsigned.

It is true that (as the name suggests) char is mostly intended to be used to represent characters. But characters in C are represented by their integer "codes", so there's nothing unusual in the fact that an integer type char is used to serve that purpose.

The only general difference between char and other integer types is that plain char is not synonymous with signed char, while with other integer types the signed modifier is optional/implied.

Ref : https://bit.ly/3esiVjT