Manipulate Array Outside Main

Question

I am trying to write a simple encryption program (Caesar cipher) and I am running into a snag. I am relatively new to the world of C and pointers, coming from Java originally.

Whenever I run the following code, it will give me the error message Segmentation fault and terminate.

I have done a little reading about what that means, but I still don't fully understand it, or what is wrong with my code, or how to remedy the issue.

If you could help with any of those things that would be greatly appreciated.

#include <stdio.h>
#include <ctype.h>
#include <string.h>

void encrypt(char *input);

int main()
{
    char *instructions = "pipi";

    encrypt(instructions);

    printf("Here are your secret instructions:\n%s\n", instructions);

    return (0);
}

void encrypt(char *input) {
    while (*input != '\0') {
        if (isalpha(*input)) {
            *input += 1;
            if (!isalpha(*input)) {
                *input -= 26;
            }
        }
        input++;
    }
}

now turn on your compiler warnings and think about why string constants are called string ***constants.*** — The Paramagnetic Croissant, Oct 20 '15 at 05:15
I'm voting to close this question as off-topic because it's trivially answerable by R'ing the FM. — The Paramagnetic Croissant, Oct 20 '15 at 05:16

score 3 · Accepted Answer · answered Oct 20 '15 at 05:18

3

String literals in C, like "pipi" are read only, trying to modify such a string will lead to undefined behavior.

Use an array if you want to modify the string:

char instructions[] = "pipi";

answered Oct 20 '15 at 05:18

Some programmer dude

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I feel very stupid. Thanks a bunch. – Michael Ziluck Oct 20 '15 at 05:19

Manipulate Array Outside Main

1 Answers1