Reverse a string in C using a function

Question

I have searched and read just for days trying to resolve this issue.

I am simply trying to reverse a string in C using my own functions, but I am stumped now and haven't been able to move forward in 2 days!

Here is my code:

/*
This program takes a string
as input and returns it to
the user but in reverse order.
*/

#include "stdio.h"
#include "stdlib.h"
#define MAXLINE 1000

/* Take in a string and return its length. */
int getline(char s[]); 

/* Copy From to To. */
void copy(char To[], char From[]); 

/* Take the contents of a string and reverse them. */
char * reverse(char s[]);

int main() {

        char mainString[MAXLINE + 1];
        copy(mainString, "Test string.");

    printf("Your string before reversal: %s\n", mainString);
    reverse(mainString);
    printf("Your string after reversal: %s\n", mainString);

    return 0;
}


int getline(char s[]) {
    int i;
    for(i = 0; s[i] != '\0'; i++);
    i++;

    return i;
}

void copy (char To[], char From[]) {
    int i;
    for(i = 0; From[i] != '\0'; i++) {
        To[i] = From[i]; 
    }; 
    To[i] = '\0';
}


char * reverse(char s[]) {

    int string_length;
    string_length = getline(s);

    char myString[MAXLINE];
    int a = 0;

    int i;
    i = string_length;

    while (i >= 0) {
        s[i] = myString[a];
        a++;
        i--;
    };
    copy(s, myString);

    return s;
}

A similar question was asked yesterday as well by someone else: http://stackoverflow.com/questions/16946115/reversing-a-string-with-strrev-c — unxnut, Jun 06 '13 at 12:58
it should be myString[a] = s[i] you are trying to reverse s right?? and add a null character to myString before copy — sethi, Jun 06 '13 at 12:59
first of all, rename getline to getlength, becasue that's what it's intended for. morevoer, remove the last i++ in this method - a string can be of length 0. — Daniel S., Jun 06 '13 at 13:01
Next time please be specific on the problem you encountered: what you expected and what did you get instead. — Balog Pal, Jun 06 '13 at 13:15

Daniel S. · Answer 1 · 2013-06-06T13:07:57.677

Remove the i++ at the end of the getline function. This caused the returned string length to be 1 more than it should be, which in turn caused a '\0' to be the first char of your reversed string, which should not happen.

Moreover, the line

s[i] = myString[a];

is wrong. This changes s, but you want to change myString instead:

myString[i] = s[a];

(Alternatively, you could do copy(myString, s); before the while loop to fill myString and then copy data from there back to s in reverse.)

score 1 · Answer 2 · answered Jun 06 '13 at 13:05

1

Fix to

int getline(char s[]) {
    int i;
    for(i = 0; s[i] != '\0'; i++);
    return i;
}

char * reverse(char s[]) {
    int string_length;
    string_length = getline(s);
    char myString[MAXLINE];
    int i, a =0;
    i = string_length-1;
    while (i >= 0) {
        myString[a]=s[i];
        a++;
        i--;
    }
    myString[a] ='\0';
    copy(s, myString);

    return s;
}

answered Jun 06 '13 at 13:05

BLUEPIXY

39,699
7
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Thank you all. I got it, espeically thanks to Bluepixy. – RHC4EVER Jun 06 '13 at 13:39

score 0 · Answer 3 · answered Jun 06 '13 at 13:06

0

The reverse function expects to reverse the string s passed in parameter and myString is local string with junk characters

So you cannot do a

s[i] = myString[a]

You just loose all the characters in s

answered Jun 06 '13 at 13:06

sethi

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Reverse a string in C using a function

3 Answers3