C, reading multiple numbers from a single line ignoring the whitespaces

Question

I am working on a problem where I need to input a line of numbers with one or more whitespaces in between and add the numbers. But I am having a problem with ignoring the whitespaces.

I have tried using scanf(" ") and scanf("%*c"). What is the most efficient way to do so?

Thanks.

Answer 1

If the number of input integers in an entered string is unknown then you can use the approach shown in the demonstrative program.

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

int main(void) 
{
    enum { N = 100 };
    char line[N];

    while ( fgets( line, N , stdin ) != NULL && line[0] != '\n' && line[0] != '\0' )
    {
        long long int sum = 0;

        const char *s = line;
        char *p = line;

        do
        {
            s = p;
            sum += strtol( s, &p, 10 );
        } while ( s != p );

        printf( "sum = %lld\n", sum );
    }

    return 0;

}

If to enter string

1 2 3 4 5

then the output will be

sum = 15

Answer 2

To read integers, use the format string %d, like this:

#include <stdio.h>

int main(void)
{
    int sum, i, n;

    sum = 0;
    n = scanf("%d", &i);
    while (n == 1) {
        sum += i;
        n = scanf("%d", &i);
    }
    printf("%d\n", sum);
    return 0;
}

If you want to read real numbers, use the format string %lf (which stands for long float) and adjust the code above accordingly.

Answer 3

The way to do it in C++ would be

double a;
double b;
double c;

std::cin >> a >> b >> c;

I am not sure if you can do something very similar in C, please tell me if that was helpful.