Stuck in a infinite loop after inputing the exit condition. - c

Question

I am trying to make this run in a loop until a non-numeric input is given. The problem is that when I input a letter to exit the while loop, it goes into an infinite loop. It also goes into the first if statement and continues to loop through that. If someone has any ideas on how to fix this, it would be great.
int counter;
int input[100]
int num = 1
while (input[num] == 0)
{
printf("score #%d:", counter);
scanf("%d",&input[num]);
if (input[num] <= 0){
printf("you cannot use negative numbers\n");
continue;
}
if (input[num] >= 100){
printf("you cannot use numbers greater than 100\n");
continue;
}
num++;
counter++;
}

Answer 1

The problem is that when scanf is provided with a non-numeric input when you try reading with %d format, the non-numeric data does not get removed from the buffer. When your loop reaches scanf again, it gets the same data, and continues failing in an infinite loop.
To fix this, remove non-numeric input when scanf does not read a proper number of items:
int readCount = scanf("%d",&input[num]);
if (readCount != 1) {
scanf("%*s");
printf("Please enter a valid number.\n");
continue;
}
Note that your loop's ending condition is incorrect, because num is always past the last element that has been read. You can fix it like this:
while (num < 100)
{
... // Read and error checks go here
if (input[num] == 0) {
break;
}
num++;
counter++;
}

Answer 2

First of all,num is supposed to be 0 as array index starts from 0 not 1.
Then,you have input[num]==0 in the condition in the while . You test using an uninitialized variable as input has not been initialized. This is the same for counter.
Your code won't compile as you have missed the ; at the end of line 2 and 3.
Lastly,replace your scanf with the following code:
if(scanf("%d",&input[num])==0)
{printf("non-numeric character entered .Exiting loop...\n");
scanf("%*s");// asterick tells scanf to discard scanned string(clear the entered char)
break;
}
So finally,the modified code:
int counter=1; // initialize variable
int input[100]; //semicolon here
int num = 0; //num must be 0
while (1) //infinite loop
{
printf("score #%d:", counter);
if(scanf("%d",&input[num])==0) //if no value is scanned
{printf("non-numeric character entered .Exiting loop...\n");
scanf("%*s");// asterick tells scanf to discard scanned string(clear the entered char)
break;
}
if (input[num] <= 0 )
printf("you cannot use negative numbers\n");
else if (input[num] >= 100)
printf("you cannot use numbers greater than 100\n");
else{
num++;
counter++;}
}