How to receive C input data until no more input?

Question

So here’s the deal:

How to receive C entries (integers) until "ENTER" is pressed?

In my program, the user must enter a chained list in the following format:

num0 num1 num2 num3 num4 num5 num6 num7 .. numN.

Ex. of list:

19 8 9 14 15 9 -9 0 7 6 5 4 -123 1.

The size of the list is unknown. It can be as many integers as the user wants to type.

How to stop the input after last number is typed?

What I need is that after enter is pressed, the program stops reading inputs.

Ex. User type: 4 5 6 7 8 9 10 and now [ENTER]. How to read the list since I use no conditions to stop the entry?

The program must accept negative, non-negative and zero integers.

Answer 1

Without a context it is not possible to offer the best solution, considering that all items will be inserted and finalized with a ENTER and only when you have a ENTER without typing anything else is that should close, one of the possible solutions can be this:

#include <stdio.h>
 
int main(void) {
    int sum = 0;
    while (1) {
        int num = -1;
        scanf("%d", &num);
        if (num >= 0) sum += num;
        else break;
    }
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

If you can accept negative numbers this solution does not work, but the question gave margin. In this case it would complicate a lot and maybe the scanf() is not the best solution, unless you use some trick.

Answer 2

You can set a point to end the reading, in case the end is the line break ENTER.

#include <stdio.h>

int main(int argc, char **argv){
    char c = 0;
    int sum = 0;
    int n;
    while(c != '\n'){
        scanf("%d%c", &n, &c);
        sum += n;
    }

    printf("%d\n", sum);

    return 0;
}

What goes on here?

The scanf takes the values directly from stdin, which is the input of values, and the stdin has the same properties as a file (has a value reserved for it).

Just like reading a file, when reading the values of stdin, the language goes through until reaching the end of the insertion, but how to define the end of the insertion?

Note that in the scanf has the following format "%d%c", when the user enters a number, he collects the number and collects the next character entered.

When the character after the number is a line break or when you hit enter, c will equal '\n', thus making the While close and all sums are added to their variable.

When the entry is made through files, the scanf can identify the latest information through having a return less than 1.

Ex:

#include <stdio.h>

int main(int argc, char **argv){
    char c = 0;
    int sum = 0;
    int n;
    while(scanf("%d",&n) > 0){
        sum += n;
    }

    printf("%d\n", sum);

    return 0;
}

Answer 3

while (scanf("%d",&num) != EOF) {
sum += num;
}

To close the entry type CTRL-D.