使用C中的递归来反转字符数组

Question

Here's my code and I can't seem to figure out how to make the function with only the array as argument.

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

int main(int argc, char *argv[]) {

      char strArray[30] = "Print this string backward.";

      puts("");
      stringReverse(strArray);

      return(0);
}


void stringReverse(char strArray[])
{ 

    if(strArray != "\n") {
        stringReverse(&strArray)
        printf("%s", strArray)
    }
}

Answer 1

A few observations and criticisms:

The math.h and stdlib.h header files are not needed for the posted code. While char strArray[30] is large enough to hold the input string, it is better to use empty brackets in a string initializer unless you need a specific size that is larger than the initial string. This is less error-prone, and just easier, since there is no need to count characters, and no need to remember to include space for the null-terminator. You probably want to move the puts(""); to after the call to stringReverse() , since this function does not print a newline character. It usually seems better to use putchar('\\n'); for something like this; putchar() is designed to print only one character, and so is the right tool for the job.

It seems that with the statement if (strArray != "\\n") {} the goal is to check if the first character is a newline, but there are a few problems with this. First, "\\n" is a string, not a character; next, strArray is a pointer to the first character of the array strArray[] , not the first character itself. There is no '\\n' character in the input string, so even if this condition were correctly written, it would always be true, and this code would enter an infinite recursion. Finally, the argument passed to stringReverse() is never changed, so there is no way for the recursion to end. For recursion to succeed, a base case must be converged upon.

A solution is to compare the first character of the array with '\\0' . If the first character is not the null-terminator, the stringReverse() function is called again, this time with the value strArray + 1 . The program will continue recursively calling stringReverse() until an empty string is passed in, at which point the final call to stringReverse() returns to its caller (the previous call to stringReverse() ), where the last character of the string is printed, before returning to its caller,.... Each of the stringReverse() frames is returned to, in the reversed order in which they were called, and each of these frames prints a character of the string, until finally the first frame is reached, and the first character is printed, before returning to main() .

Note that in a function call, and in fact most expressions, arrays decay to pointers to their first elements. So, in stringReverse() strArray is a pointer to char that points to the first element of the array provided as an argument by the caller. Also note that in a function declaration such as void stringReverse(char strArray[]) array types are adjusted to appropriate pointer types, so this declaration is equivalent to void stringReverse(char *strArray) .

#include <stdio.h>

void stringReverse(char strArray[]);

int main(void)
{
    char strArray[] = "Print this string backwards.";

    stringReverse(strArray);
    putchar('\n');

    return 0;
}

void stringReverse(char strArray[])
{
    if (*strArray != '\0') {
        stringReverse(strArray + 1);
        putchar(*strArray);
    }
}

Program output:

.sdrawkcab gnirts siht tnirP

Answer 2

First, you need to return an value.

Then, what your algorithm should to do? Run until the final of your string and then return variable by variable in reverse with just one parameter, well you just need pass this parameter shorter every loop.

Like this:

#include "stdafx.h"
#include "stdio.h"
#include "stdlib.h"
#include "string.h"

void stringReverse(char strArray[], int i) {
    if (strArray[0] != NULL)
    if (strArray[0] != '\0') {
        int c = 0;
        char str[30];
        while (c < strlen(strArray)) {
            str[c] = strArray[2 + c -1];
            c++;
        }
        str[c] = '\0';
        stringReverse(str);
    }           
printf("%c", strArray[0]);
}

int main(int argc, char *argv[]) {
    char strArray[30] = "Print this string backward.";
   stringReverse(strArray, 0);
   printf("\n\n");
   system("Pause");
   return(0);
}