Thread: C program with arrays, while loop, and sentinel value

Originally Posted by jimblumberg

You need to insure that you properly initialize all of your variables.

Also your while loop is a little messed up. Remember you're checking for the sentinel value at the start of the loop, so you should be getting your user entries right before the loop ends. Something like:

Code:

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

#define SIZE 50

int main()
{
    int value = 0, arr[SIZE] = {0}, i = 0;  // Don't forget to initialize all of your variables.
    printf("Enter up to 50 numbers. Type and enter -999 to stop the loop: ");

    // You need to get the first value from the user prior to the while loop.
    scanf("%d", &value);

    while (i < 50 && value != -999) // Notice the change here.  
    {
        arr[i] = value;
        printf("%i = %i \n", arr[i], value);

        printf("Enter another number. Type -999 to stop the loop: "); // keeps being printed with the other printf
        scanf("%i", &value);

        i++;
    }
    return 0;
}

Thank you, that solved most of the issues.
Now the only problem is that 'i' isn't incrementing. I need it to start at zero and end at 49. Is 'i' in the incorrect place?

Code:

#include <stdio.h>
#include <stdlib.h>
#define SIZE 50
int main()
{
    int value = 0, arr[SIZE] = {0}, i = 0;  
    
    printf("Enter up to 50 numbers. Type and enter -999 to stop the loop: ");
    scanf("%d", &value);
    while (i < 50 && value != -999){
     i++;
        printf("arr[%i] = %i \n", arr[i], value);
        printf("Enter another number. Type -999 to stop the loop: ");
        scanf("%i", &value);
    }
    
    return 0;
}

Originally Posted by userxbw

place your i++ on the last line in your loop, the way you have it it is incrementing before you add it to your arr so you're going to end up one short.


a good way to trouble shoot your issues is using printf to print out the values you're working with so you can see what is going on with them. then you should be able to discern them better.

That is a brilliant idea. I did so and I see that 'i' does not add one to itself. Do I need to add 'i += 1'?

Code:

#include <stdio.h>
#include <stdlib.h>
#define SIZE 50
int main()
{
    int value = 0, arr[SIZE] = {0}, i = 0;  
    
    printf("Enter up to 50 numbers. Type and enter -999 to stop the loop: ");
    scanf("%d", &value);
 i+=1;
 // printf("%i \n", i); i is 1 but turns to 0?
 // need i to start at 0 and add one
 
    while (i < 50 && value != -999){
        printf("arr[%i] = %i \n", arr[i], value);
        printf("Enter another number. Type -999 to stop the loop: ");
        scanf("%i", &value);
        i++;
        // printf("%i \n", i); 
        // i staying as 0l
    }
    
    return 0;
}

Originally Posted by userxbw

with your i on top it sets i = 1 so your array [ 0 ] never gets a value inside of it.
whence you got that corrected leave it alone .

Code:

#include <stdio.h>
#include <stdlib.h>
 
#define SIZE 50
 
int main()
{
    int value = 0, arr[SIZE] = {0}, i = 0;  // Don't forget to initialize all of your variables.
    printf("Enter up to 50 numbers. Type and enter -999 to stop the loop: ");
 
    // You need to get the first value from the user prior to the while loop.
    scanf("%d", &value);
 
   while (i < 50 && value != -999) // Notice the change here.  
    {
        printf("loop i set to 0 at start\non top of loop i = %d\n", i);
        arr[i] = value;
        printf("arr [ %i ] = value = %i i = %d\n", arr[i], value, i);
        i++; 
        printf("on bottom of of loop i = %d\n", i);
        printf("Enter another number. Type -999 to stop the loop: "); // keeps being printed with the other printf
        scanf("%i", &value);        
    }
    
    
    
    int j = 0;
for ( ; j < 50; j++)
    printf("%d arr\n element number %d\n", arr[j], j);
    
    return 0;
}

I think I got it! thank you sir

thanks goes to jimblumberg as well.