How can I use for loop to scan unknown number of inputs in c using an array. I don't know what to put in the for loop

I tried this

#include <stdio.h>
int main() {
    int in[100];
    for (int i = 0;; i  ) {
        scanf("%d", &in[i]);
        if (in[i] == -1) {
            break;
        }
    }
}

CodePudding user response：

You need to be able to tell when the input is done. You can either read all input until stdin is at EOF or let the user enter a specific value that means "stop, I have no more input". It seems you've chosen -1 to mean "stop".

In your case, the loop should have been:

int i;   // declare i before the loop to be able to use it after the loop
for (i = 0; i < 100; i  ) {   // note: check the boundary 100
    // check that scanf succeeds too:
    if(scanf(" %d", &in[i]) != 1 || in[i] == -1) {
        break;
    }
}
printf("you entered %d number of values\n", i);   // i used after the loop

You may also want to allocate the memory dynamically. Using an array of, say int[100], will not be enough if the unknown amount turns out to be 101.

Here's an example where the user is asked to enter any number of integers. Entering -1 will exit the loop.

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

int main() {
    puts("Enter integers (-1 to stop): ");

    int *in = malloc(sizeof *in); // allocate space for 1 int
    unsigned count = 0;

    while(scanf(" %d", &in[count])==1 && in[count] != -1) {
          count;
        // allocate space for one more int:
        int *np = realloc(in, (count   1) * sizeof *np);
        if(np == NULL) {
            puts("Can't allocate more memory. What you entered so far will have to do");
            break;
        }
        in = np;
    }

    printf("you entered %d number of values\n", count);
    for(unsigned i = 0; i < count;   i) {
        printf("%d\n", in[i]);
    }

    free(in);
}

CodePudding user response：

I tried this `

#include <stdio.h>    
int main()    
{    
int in[100];    
for (int i=0;;i  )    {    
    scanf("%d", &in[i]);    
    if (in[i] == -1)    {    
        break;    
    }    
}    

}`