Thread: while loop with array

why wont this loop exit after I have typed a negative number?

Code:

int main()
{
int scores[10]={0,0,0,0,0,0,0,0,0,0};
int ids[10]={0,0,0,0,0,0,0,0,0,0};
int i;

for(i=0;i<10;i++)
printf("scores are %i\nand IDS are %i\n\n", scores[i], ids[i]);

i=0;

while(ids[i]>=0)
{
                scanf("%i", &ids[i]);
         printf("scores are %i\nand IDS are %i\n\n", scores[i], ids[i]);
         i++;      
               
               }

    system("pause");
 return 0;   
}

Because at the end of the loop, you increment i, so it's no longer the index of the negative number you typed.

You are checking the currently what's in the array not the input value.

you're just replacing the ids[i] till you a seg fault because there is no bound

so should i increment 'i' before I input?

Nope. In C, if you have an array with 10 elements, the valid indexes are 0 to 9. This is how you are currently storing the elements, but the problem is, after you store the element, you check the next element to see if it's less than zero, so you miss the negative number you entered. Try something like:

Code:

i = 0;
do {
    if (i == 10)
        break;  // don't allow more that 10 numbers, otherwise there's an overflow
    scanf("%i", &ids[i]);
    printf("scores are %i\nand IDS are %i\n\n", scores[i], ids[i]);
} while (ids[i++] >= 0);

A more straightforward solution that avoids the use of the break statement is to to alter the while statement's conditional test:

Code:

    i = 0;

    while ( i < 10 ) {
        scanf( "%i", &ids[i] );
        printf( "scores are %i\nand IDS are %i\n\n", scores[i], ids[i] );
        i++;
    }

Kevin

Originally Posted by kmess

A more straightforward solution that avoids the use of the break statement is to to alter the while statement's conditional test:

But then he loses his exit on -1...

Code:

    int ids[10] = {0};  // intialize to 0 and avoid influence on outcome

    i = 0;

    while ( i < 10 ) {
        scanf( "%i", &ids[i] );
        if (ads[i] < 0)
            { ads[i] = 0;
               break; }
        printf( "scores are %i\nand IDS are %i\n\n", scores[i], ids[i] );
        i++;
    }

Plus this still doesn't do anything with the scores array....

Indeed, but my comment focused solely on the conditional test expression and the elimination of the break statement proposed earlier, not on the program as a whole.

Kevin

The only problem is, he needs to stop the loop if it's full or if he's entered a negative number. I suppose if you wanted to avoid the use of a break statement, you could do something like the following:

Code:

int i, arr[MAX];
i = 0;
do {
    printf("Enter a number, negative to stop: ");
    scanf("%d", &arr[i]);
    i++;
} while (i < MAX && i > 0 && arr[i-1] >= 0);

EDIT: What Tater said...I'm slow today.

Originally Posted by kmess

Indeed, but my comment focused solely on the conditional test expression and the elimination of the break statement proposed earlier, not on the program as a whole.

Kevin

So... now you're telling us you're narrow minded?