array, isdigit function, while loop

Question

This a C program that I wrote for an assignment. I just wanna add some lines of code of my own. But it ended up in a never-ending loop.

I tried using a while loop to solve this, but that is where my problem is.

int tab1[6],c;

printf("\n\nEnter 4 integers in the first array:\n ");

for (c = 0; c < 4; ++c)
{
    printf("\n\tValue %d : ",c+1);
    scanf("%d",&tab1[c]);
        //if tab1[c] is not a number ask again.
            while (!isalpha(tab1[c]))
            { 
                printf("nEnter an integer : ");
            }
            scanf("%d",&tab1[c]);

}

I wanted for the program to ask out for an integer when the user enter something other than an integer.

Even if what you were trying to do could work, you have the second `scanf` outside the `while` loop. Since the condition being tested never changes, you get an infinite loop. — Barmar, Apr 19 '19 at 17:25

score 0 · Answer 1 · answered Apr 19 '19 at 17:24

You need to do the conversion from string to number after getting the input. I mean: first input, then check and convert.

// 1st: input
if (!fgets(buf, sizeof buf, stdin)) /* error */;
// 2nd: check and convert
if (sscanf(buf, "%d", &tab1[c]) != 1) /* error */;

scanf() is already doing that on its own, but you maybe want something more powerful.

You want to use the return value of scanf() to know whether it converted successfully:

if (scanf("%d", &tab1[c]) != 1) /* error */

array, isdigit function, while loop

1 Answers1