program using char and string is working weirdly

This is a discussion on program using char and string is working weirdly within the C Programming forums, part of the General Programming Boards category; Code: #include <stdio.h> #include <string.h> int main (int argc, char *argv[]) { int i=0; int input=0; char str1[i]; char str2[i]; ...

  1. #1
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    program using char and string is working weirdly

    Code:
    #include <stdio.h>
    #include <string.h>
    int main (int argc, char *argv[]) {    
    
        int i=0;
        int input=0;
        char str1[i];
        char str2[i];
        int n;
    
        printf("Please enter shift [0--25]: %d %c \n", input, str1[i]); //read a number between 0 and 25 and then read a list of characters
        n=scanf("%c", &str1[i]);
    
        i=0;
        while (str1[i] != '\0') {
            str2[i] = str1[i];
            i=i+input; //This will shift the string of characters by the read number's value
        }
        str2[i] = '\0';
        printf("%c", str2[i]);
    
        return n;
    }


    The above is the program I wrote. The output should be the following for example:



    Please enter shift [0--25]: 5
    abcd (what the user types in)
    fghi (what comes out, a + 5 = f, b + 5 = g, etc)
    ctrl d
    Thank you for any help

  2. #2
    and the hat of wrongness Salem's Avatar
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    > int i=0;
    > char str1[i];
    > char str2[i];

    How much space is allocated to your arrays - none.

    > printf("Please enter shift [0--25]: %d %c \n", input, str1[i]);
    What was str1 initialised to before printing it - nothing.

    You probably want something like str1[100] and %s for reading in a string.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
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    Thank you for that. I have made a few adjustments, however, it still isn't working as planned. Because the following error message won't let me compile it:
    invalid operands to binary & (have 'int *' and 'int') //reference to line 12

    Code:
    #include <stdio.h>
    #include <string.h>
    int main (int argc, char *argv[]) {    
    
        int i=100;
        int input=0;
        char str1[i];
        char str2[i];
        int n;
    
        printf("Please enter shift [0--25]: %d %c \n", input, str1[i]);
        n=scanf("%d %c", &input &str1[i]);
    
        i=0;
        while (str1[i] != '\0') {
            str2[i] = str1[i];
            i=i+input;
        }
        str2[i] = '\0';
        printf("%c", str2[i]);
    
        return n;
    }
    Last edited by kase20; 04-21-2012 at 11:06 PM.

  4. #4
    Algorithm Dissector iMalc's Avatar
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    Why do you insist on putting [i] in every place after str1?

    In a declaration the number in the square brackets specifies the size of the array,
    whereas elsewhere it means that you want to access the item with the number specified.


    Given an array of size 100 only has valid indexes 0 to 99, you're going out of bounds. Subsequent code goes way out of bounds in fact.
    You need to understand and learn the part in bold.
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