What are variadic functions (va_list) in C?

main.c

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

int sum(int count, ...) {
    va_list args;
    va_start(args, count);

    int s = 0;
    int i;
    for (i = 0; i < count; i++) {
        int x = va_arg(args, int);
        s += x;
    }
    va_end(args);
    return s;
}

int sum2(int a, ...) {
    va_list args;
    va_start(args, a);

    int s = a;
    int i;
    int x = va_arg(args, int);

    while(x != 0) {
        s += x;
        x = va_arg(args, int);
    }

    va_end(args);
    return s;
}

int main(int argc, char *argv[]) {
    printf("Sum is: %d\n", sum2(1, 2, 3, 4, 0));
    return 0;
}

Quickstart guide for C pointers

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