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 : Welcome to w3resource.com.
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:

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
What is the size of an enum in c?
An enum is only guaranteed to be large enough to hold int values. The compiler is free to choose the actual type used based on the enumeration constants defined so it can choose a smaller type if it can represent the values you define. If you need enumeration constants that don't fit into an int you will need to use compiler-specific extensions to do so.
Ref : https://bit.ly/3ypg4k8
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