12-21 Lab exercise 3: Fix the program with basic Pointer

Question

In the following program, we want to stores two strings in two arrays, swaps them, and displays their new content. There some error. Please fix it and explain why and how in the comment after your answer.

#include <stdio.h>
int main(){
    char temp[100];
    char str1[100] = "Let see";
    char str2[100] = "Is everything OK?";
    temp = str1;
    str1 = str2;
    str2 = temp;
    printf("%s %s", str1, str2);
    return 0;
}

 

Answer 1

Hidden content!
#include ** **       * *
int main(){
* * *  ***  *  * *  *  **** * *temp;
* **** *  * *** *** **** *** *  * * *str1 =   ** ** * *  **  * ******
    *  * ** * **   * *** * **  *str2 = *  *   * everything     **
* **  ***   * **   * *    **  ** = str1;
 * **  ** ***** * *    ****  = str2;
***  * ** *  **       *       * = temp;
* ***   * * **  * * ** **** ****      * ** *** **  **  str1, str2);
   ***  * ** *  ****  ******    *   0;
}

Comments

Case 0: Correct output

Answer 2

Hidden content!
  *  *   ** * **  *  ** *
int    **
 * * *  * *   ****  *** **** **** * **
 ******* **   ***** ****     ** *  * ***  ***  * *   * *  
     * *  **   *** **** *  *    ***   *     * **  ***
* **  *  *** * * *  **   ** *****    is      * to **  **** char[] need to be ***** string or     ** * ** *
 **** ***   **  **    *** **    **  * * *   ***  *    *  assign to *** *  *
    * *** * ***   * *** *   ******  * is   for each char * **      a  **    **** is an array of   ***
  *     *** *    ** **** * ** an array has 6  ***** *  the        the value of str1 is the *** * of the first     * 
*   *  * * * *  *  *     *      *  = str1;
         *   * ** **  *** = str2;
*  ***    *    ** ** ***   ***    ** = temp;
 ****   *   *     *  * **   ***   *  ** ***     *  **  ****  str1, *   
*  *   **  * * *   ** *  * * * ** 0;
}

Comments

Case 0: Correct output

Answer 3

Hidden content!
 ****   **  *** 
int * *
* * * * **** ** *  **    *  * ****
 ** ** * *   * * * **** * *  ***  * * ** *  **** *
**  * *** * *  *   * * * * *    ** * ** ** **    * *  ***
 *     ***** *  **  ** *    ***** **** is   * to * *  char[] need to be * *  string or *    ** *    *  
**       * ****       *  *  ** ***  *   ** *   assign to     ***
 **  ** **     * * * ** ** ***     is *** for each char   *   * a  *    * * is an array of * * * 
* * * *  **  * ****  **** * ** **   an array has 6 * *  *  * the * *  the value of str1 is the   ** of the first * * 
  * *   *  *    * ***  *    *****  = str1;
*   *      * * * ** **** * ** * * = str2;
  *    *  **** * *     ***      = temp;
**    *** *  *  *       ** ***     ***  * ** *    ** str1, ** *
** * ***   **    * * **  **  0;
}

Comments

Case 0: Correct output

Answer 4

Hidden content!
#include      * *  * *** * 
int main(){
* * *** * *   **** * **** *  *  *temp;
 ***    ** **** *   *     ** *str1 = *  ***    **  *** 
 * * * *   * *  * **  * * *str2 =       everything * **** 
 ** *  *  ***     *   **  *      = str1;
 **   ** ***** **   ***  ***** = str2;
* * *** *   ** * *  * **** *** *** = temp;
     * ** *     *  ****** *   *    *** * * str1, str2);
 *    * *     ****  * * * **  0;
}

Comments

Case 0: Correct output

---

因為arry不能改變位置
只有pointer 可以
所以把全部都改成指標就可以了

Answer 5

Hidden content!
#include  **   * **  * * 
int main(){
 **   *  * ** *  ** ** * * **     *temp;
*  *  *******    *  *   *    * *str1 = *     ** **  *  ** 
***    * *  ****  * *  ** ** *str2 = **      everything  ****  
*** ** ** ** ****  *****  * *   = str1;
 *  ***** * * ***  *   **** ** = str2;
 **** **  * ** * * *   *  = temp;
  *  * *   * *     **   * *  * *    * *     * *******  str1, str2);
 ******* *   ***    * *   ***** 0;
}

Comments

Case 0: Correct output

---

Explain:
  First, the type of "temp=str1" is pointer but  the head of main is array, so it can't work.
But if we use the array to solve this problem, we may have to use the for root to exchange every characters.
So we use the pointer, it's easy to use the pointer to exchange the string
So we set the array to pointer to solve the problem.

Answer 6

Hidden content!
#include  *    * *    ** *
int main(){
 * *    ****   * * **   ** ** *temp;
**   **** * *  **  *     *str1 =       *  *    *****
  ***  *****    ** ***  **  *str2 =  *  *    everything ** ** * *
 **  * *   *  *   * ** *  = str1;
    * *      *****  * * *      = str2;
**  *** * **  ** *   *  *** *   = temp;
   * **   ****  ***   **  * **   ***  *   *     ** str1, str2);
  **  * ******  *   ****   ** * 0;
}

Comments

Case 0: Correct output

Answer 7

Hidden content!
*    ** * *** ** * **
int   *
 * **** * * *** * * * ***  * ****
 **  **  ** **  * **  * *  ****  *str1 =  **  ****  *  
*  *  * ** ***    *    *   *str2 = *  ** **  * ***         
* **** ***  ** *** *** * = *** 
* ** ** **   *****        ** * = str2;
 *  **   ***  *** ***  *   * * **  =    
  ***  *   * * **   ****  * * * *    ***    * ** *   * *** *
   ***** ****  * **  *   ** ** * 0;
}

// The *  *  was in the     **  
//the  **    can only **       one  ** *  *   *  and  ** * 
//but array is a  * * of *** **   (or      and etc)

Comments

Case 0: Correct output

Answer 8

Hidden content!
#include * *   ** * * ****
int main(){
 *    *    ***** * *** ***   ** ** *temp;
 *   **** ***   ** ****** *  *str1 =   **   **  * ******     
 *   ** *** *  *  ** **  * * *  **    *str2 =  *  ***  everything  *  ****   
**  ** *   *   *  ****   *   ** = str1;
* **      * * *   *  * *** = str2;
 * *  *    **** * ** *    * * = temp;
*   ****    *    ***    **       ** ***  * str1, str2);
* ** *  * *  **   * * ***  0;
}

Comments

prog.c: In function 'main':
prog.c:6:5: error: 'temp' undeclared (first use in this function)
     temp = str1;
     ^~~~
prog.c:6:5: note: each undeclared identifier is reported only once for each function it appears in
prog.c:6:12: error: 'str1' undeclared (first use in this function)
     temp = str1;
            ^~~~
prog.c:7:12: error: 'str2' undeclared (first use in this function)
     str1 = str2;
            ^~~~

---

Case 0: Correct output

Answer 9

Hidden content!
#include  ***  * *   **
int main(){
   * *** *** * *** *** ** **   ** *
*** *****  *  **   *  *  *  str1[100] = **  ** * * * *  * 
 *  *      ***** *  *  *       str2[100] =  *****   **  ** **

**  *        **    **   **   *    *** ** * **   ** * str2, str1);
  * * * *****   ****          0;
}

Comments

Case 0: Correct output

---

Case 0: Wrong output

---

Case 0: Correct output

Answer 10

Hidden content!
#include ** **** * * ******    
int main(){
** **   ***   * * *  * *** *   *temp;
 *  **     * *   * *   * * *str1 =  ***    *  *****  *  
**** * **  **   ***  ** *   * * *str2 = *  everything   ** ** *** 
  * * * *** ** *  *** * *    = str1;
 ** * * **********   *   * = str2;
*****      **** * **   ***** = temp;
*  ***    ** **   ********  ***        **     str1, str2);
**   ***   *  *  ****  **  **     0;
}

Comments

Case 0: Correct output