为什么我的程序为什么在向数组赋值的语句中退出循环？

Question

I wrote a simple program to print the Fibonacci series up to a certain value, store it in an array and calculate it's sum.

#include<stdio.h>
int main()
{
    int i,a=0,b=1,c,limit,sum=1;
    int fib[limit];
    printf("Enter the number of terms: \n");
    scanf("%d", &limit);
    fib[0]=0;
    fib[1]=1;
    printf("0 \n");
    printf("1 \n");
    for(i=2; i<limit; i++)
    {
        c=a+b;
        printf("%d \n",c);
        fib[i]=c;
        a=b;
        b=c;

    }
    for(i=0; i<limit; i++)
    {
        sum+=fib[i];
    }
    printf("The sum is %d", sum);

    }

But it doesn't output the series until the limit and I believe this line may be the cause.

fib[i]=c;

I'm not sure why though. Could you please help me?

Thank You

Answer 1

int fib[limit];
printf("Enter the number of terms: \n");
scanf("%d", &limit);

will be

printf("Enter the number of terms: \n");
scanf("%d", &limit);
int fib[limit];

Otherwise you were declaring the VLA with a variable having indeterminate content. This is undefined behavior. In your case program crashed when you tried to use it.

In case you are in C89 then you need to initialize the size with some maximum value as VLA is not supported in C89.

void MAXLIMIT 1000
...

int fib[MAXLIMIT];

Answer 2

int i,a=0,b=1,c,limit,sum=1;
int fib[limit]; printf("Enter the number of terms: \n");
scanf("%d", &limit);

limit isn't initialized when you declare the variable length array fib . limit could be any value at all. This means that the length is unknown, which will surely cause problems. It's undefined behavior.

Also, I noticed that you tagged this with C89. In the 1989 standard variable length arrays are not allowed. Any standards compliant compiler will refuse to compile this, or at the very least emit a stern warning. VLAs are permitted in the C99 standard though.

int i,a=0,b=1,c,limit,sum=1;
printf("Enter the number of terms: \n");
scanf("%d", &limit);
int fib[limit];

If you did it like this, it would work fine, and be perfectly valid C99. C89 still wouldn't work because of the VLA and the fact that fib isn't defined before printf and scanf .

Answer 3

There are some mistakes in your code .

The limit value contain the garbage value at this line

.....
int i,a=0,b=1,c,limit,sum=1;
....

& then you initialize an array with the size of garbage value .

....
int fib[limit];
....

after that you take the 'limit' value as the size of array.

....
printf("Enter the number of terms: \n");
scanf("%d", &limit);
....

but you can initilaize the array before taking the limit value .

so the correct code is ,

    ....
    printf("Enter the number of terms: \n");
    scanf("%d", &limit);
    int fib[limit];
    ....

You have initialze the array after taking the size of array as named 'limit'

Now you code will work perfectly .& sum of Fibonacci series correctly evalutaed.