Help with reversing a string in C

Question

I am trying to reverse a character string in C

Here is what I have

void reverse(char str[]) {
    int i = 0;

    int length;
    // Get string lengt         


        

Answer 1

You can use either of the two methods below, depending on whether you're comfortable with pointers or not. It will also be worthwhile looking at them side-by-side when you satrt learning about pointers so you can better understand how they map to each other.

This is a full program for testing purposes:

#include 
#include 

// The pointer version.
void reverse1 (char *str) {
    char t;                      // Temporary char for swapping.
    char *s = str;               // First character of string.
    char *e = &(s[strlen(s)-1]); // Last character of string.

    // Swap first and last character the move both pointers
    // towards each other. Stop when they meet or cross.
    while (s < e) {
        t = *s;
        *s++ = *e;
        *e-- = t;
    }
}

// The array version.
void reverse2 (char *str) {
    char t;                // Temporary char for swapping.
    int s = 0;             // First character of string.
    int e = strlen(str)-1; // Last character of string.

    // Swap first and last character the move both pointers
    // towards each other. Stop when they meet or cross.
    while (s < e) {
        t = str[s];
        str[s++] = str[e];
        str[e--] = t;
    }
}

 

int main (void) {
    char x[] = "This is a string for reversing.";
    printf ("Original: [%s]\n", x);
    reverse1 (x);
    printf ("Reversed: [%s]\n", x);
    reverse2 (x);
    printf ("   Again: [%s]\n", x);
    return 0;
}

and the output is:

Original: [This is a string for reversing.]
Reversed: [.gnisrever rof gnirts a si sihT]
   Again: [This is a string for reversing.]