Looping

[timeless]

I just need help with finishing off this simple program i made that applies the ROT13 process to the string entered. It all works fine but i can't get it to loop properly..

I want to after running through the program once prompt the user again asking if they would like to enter another string and if so it would loop through the program again.. if not it would end. i have tried a do while loop but it just doesn't work.

Here's the code:

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

void readin(char str[])
{

	printf("Enter string:\n ");
	scanf("%s", str);
	
	return;
	
}
			
void rot13(char str[])
{
    int i;
    for (i = 0; i < strlen(str); i++)
    {
        if (isupper(str[i]))
        {
            if (str[i] <= 77)
                str[i] += 13;
            else
                str[i] -= 13;
        }
        if (islower(str[i]))
        {
            if (str[i] <= 109)
                str[i] += 13;
            else
                str[i] -= 13;
        }
    }

	
	return;
}

void print(char str[])
{
	printf("The String is now: %s\n", str);
	
	return;
}

void goagain(char loop)
{
	printf(" would you like to enter another string? y or n:\n ");
	scanf("%c", &loop);
	
	return;
}

int main()
{	
		const int MAXSIZE = 100;
		char str[MAXSIZE] = {'\0'};
		char loop;
		
		
	do{
		readin(str);
		rot13(str);
		print(str);
		goagain(loop);
		
	}while(loop != 'n');
		
	
	return(0);
}

[tabstop]

The function goagain has no way of affecting the value of loop in your main program. (It can affect the value of its own variable called loop, but those are not the same variable.) You may want to have goagain return the char instead.

[timeless]

hmmm i tried it just then.. still doesn't work..

char goagain(char loop)
{
	printf(" would you like to enter another string? y or n:\n ");
	scanf("%c", &loop);
	
	return(loop);
}

[tabstop]

Changing it there is only half the battle -- did you make the appropriate changes in your main as well?

[timeless]

the only change i made was loop = goagain(loop).. not sure what else i can do =\ I'm really stuck, never had this much trouble getting a loop to work.

int main()
{	
		const int MAXSIZE = 100;
		char str[MAXSIZE] = {'\0'};
		char loop;
		
		
	do{
		readin(str);
		rot13(str);
		print(str);
		loop = goagain(loop);
		
	}while(loop != 'n');
		
	
	return(0);
}

[tabstop]

Try

scanf(" %c", &loop);

, which will keep out any stray enter-key presses.

[timeless]

thanks so much works perfect.

[CommonTater]

thanks so much works perfect.

Now that you have it working, why don't you try to refine it...

char goagain(char loop)
{
	printf(" would you like to enter another string? y or n:\n ");
	scanf("%c", &loop);
	
	return(loop);
}

You aren't using the passed in value inside the function, so there's no need to pass in a value.
It's bad ju ju to use a variable passed in to hold the results of a calculation, especially one done by pointers.

So get rewrite the function to not take any parameters and declare a local variable to hold the result of scanf().

Second returning the character works, but it might be better to return true or false (1 or 0).

Once you have it doing that, you can move the function call directly into your while statement...

int goagain( void )
{  char loop;
    printf(" would you like to enter another string? y or n:\n ");
    scanf(" %c", &loop);
    return tolower(loop) == 'y';  // returns true if y or Y false for everything else
}



// in main
  do
   {  readin(str);
     rot13(str);
     print(str);
   }while(goagain());

Half the fun of programming is simplifying and cleaning up code... the time to start forming these good habits is when you are just starting out. The alternative is that later on you will spend half your time fixing up after bad habits...