Thread: help on loop

its not working

Show your current code.

any way you got any idea on how to do this in other way? where if i keyin -1 it will terminate the program..

Yes, but you should try and come up with it yourself. As I suggested, if you are having trouble solving your entire problem at one go, break it down into parts and solve each part separately, then combine the knowledge you gain from solving them separately to help you solve the entire problem.

You should indent it properly, e.g.,

Code:

#include<stdio.h>
#include<string.h>

int main()
{
    char strsrc[5];
    char strtmp[5];

    printf("\n Enter a five-digit number ( -1 to end ): ");
    gets(strsrc);

    strcpy(strtmp,strsrc);
    strrev(strtmp);
    while (strcmp(strcmp, "-1") !=0) {
        if(strcmp(strsrc,strtmp)==0)
            printf("\n &#37;s is a palindrome\n",strsrc);
        else
            printf("\n %s is not a palindrome\n",strsrc);
    }

    return 0;
}

Now, where is strrev() defined? As far as I can tell, you are trying to use a function that does not exist. Even before implementing your while loop, this should have come to your attention.

Stop what you are doing right now and complete the tasks that I outlined. You are clearly jumping into the problem without making effort to break it down into parts and confirm that the individual pieces are working before integrating them. At this rate, you have no hope of finishing this simple problem since any attempt to fix the loop will not fix the problem as you are not even reversing the string, and any attempt to fix the string reversal will not fix the problem since the loop is incorrect.

Oh, and you really should not be using gets(). Use say, fgets() instead (and you will discover that you actually want strsrc and strtmp to have 6 chars, not 5).

EDIT:
Actually, since you already have some idea of how to use strcmp(), you could actually accelerate working through the smaller tasks:

• Write a program that reads in a word of no more than 5 letters and prints the word in reverse.
• Write a program that reads in a word of no more than 5 letters and prints "Yes!" if the word is a palindrome, otherwise print "No!".
• Write a program that reads in words of no more than 5 letters. While the word is not "-1", print the word and read another word, otherwise end the program.

So your final program would basically be: write a program that reads in words of no more than 5 letters. While the word is not "-1", (print "Yes!" if the word is a palindrome, otherwise print "No!") and read another word, otherwise end the program.

Nonetheless, resist the urge to jump tasks.

strrev <<< this mean revers the caracter so that i can compare with the origenal one witch is user have keyin

Be warned that strrev() is not in the standard C library.

then what are other method that i can use?

Implement it yourself. Actually, you do not need to reverse the entire string to determine if it is a palindrome... but perhaps you can change this later.

Anyway, we are making circles here. Here is what you want (even though I already posted it)
Try this and it will end properly.
But AGAIN, you have MORE errors. So do this:

Code:

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

int main(void) {
   char strsrc[6];
   char clean[100];
   while(1) {
       printf("Enter 5 digits or -1 to exit: ");
       fgets(strsrc, 6, stdin);
       if (strcmp(strsrc, "-1\n") ==0) break; //exit while
       printf("OK\n"); //otherwise print OK
       fgets(clean, 100, stdin); //clean remaining characters
   }
}

the above will print OK until you press -1. You NEED to clean the remaining characters. If you don't, then if somebody enters 5 digits the \n will remain (since they pressed enter). So next time that will be read. To avoid this, you call one more fgets() which will read everything that is left and "clean" stdin. If somebody enters more than 5 digits, then the first five will be read and the remaining will be cleaned. In any way this should work for you for (almost, don't try to prove me wrong) all input.

EDIT: fgets reads also the \n, so if you enter -1 you will actually have "-1\n". So I changed the strcmp to include this

fgets(strsrc, 6, stdin);

I prefer
fgets(strsrc, sizeof strsrc, stdin);
so no question arises what is magic 6
and also no problem could appear if the size of the array is suddenly changed

//clean remaining characters

if the string was read fully - this call will require user to press enter once again - better to check that the \n is not present in the strsrc buffer before calling this "cleaning" fgets