C程序中的斐波那契数列，其中第一个2数字由用户给出

Question

When the first number is 1 and second number is 2 , and the length is 5 , it should be 1 2 3 5 8 . But then my output is always 1 2 1 3 4 . I can't seem to find the problem.

Another input is 2 and 5 . Output is 2 5 1 6 7 . The 3rd number which is 1 shouldn't be there. What should I change or add?

*This is already a submitted HW and yes its wrong I got the deductions already. Now I just want to fix this so I can study this.

int main()
{
  int i, lenght = 0, fib, sum, sum1, sum2, a, b, c;
  printf("\nFirst number: ");
  scanf("%d", &a);
  printf("\nSecond number: ");
  scanf("%d", &b);
  printf("\nHow long?: ");
  scanf("%d", &lenght);

  {
    while ((a > b) || ((lenght < 2) || (lenght > 100)))
    {
      printf("\nFirst number: ");
      scanf("%d", &a);
      printf("\nSecond number: ");
      scanf("%d", &b);
      printf("\nHow long?: ");
      scanf("%d", &lenght);
    }
  }

  printf("%d\t%d\t", a, b);
  printf("%d\t", fib);
  for (i = 3; i < lenght; i++) {
    if (i <= 1) fib = i;
    else {
      a = b;
      b = fib;
      fib = a + b;
    }

    printf("%d\t", fib);
  }
}

Answer 1

第一次打印fib （在for循环之前），您尚未分配任何内容。

Answer 2

just add fib=a+b; before printing fib value. Its a good coding habit to initialize all variable before using it(especially in C).

Answer 3

Your code seems strange to me. I tried to simplify your code a bit. See this once:

int main()
{
    int a,b,next,last,i;
    printf("Enter the first Value:");
    scanf("%d",&a);
    printf("Enter the second Value:");
    scanf("%d",&b);
    printf("Enter the length of Fab. series:");
    scanf("%d",&last);
    printf("%d,%d,",a,b);
    for (i=3; i<= last; i++)
    {
    next = a + b;
    if(i<last)
    printf("%d,",next);
    else
    printf("%d",next);
    a = b;
    b = next;
    }
    return 0;
}

Hope it's Helpful!!

Answer 4

Since this is for study, issues with your code: you don't need to duplicate the calls to scanf() , simply initialize one of the variables to fail (which you did: lenght = 0 ) and let the loop do its thing; pick one indentation style and stick with it; if you're new to C, always include the curly braces, even when the language says they're optional; you (correctly) allow for a length of 2, but then print three numbers; your if (i <= 1) clause is a no-op as the loop starts with for (i = 3; so i is never less than 3.

Putting it all together, we get something like:

#include <stdio.h>

int main() {
    int length = 0, a, b;

    while (length < 2 || length > 100 || a > b ) {
        printf("\nFirst number: ");
        (void) scanf("%d", &a);
        printf("\nSecond number: ");
        (void) scanf("%d", &b);
        printf("\nHow long?: ");
        (void) scanf("%d", &length);
    }

    printf("%d\t%d\t", a, b);

    for (int i = 2; i < length; i++) {
        int fib = a + b;

        printf("%d\t", fib);

        a = b;
        b = fib;
    }

    printf("\n");

    return 0;
}

Note that the input error checking isn't sufficient to prevent problems. Eg b can be greater than a , but still mess up the sequence if you input random numbers. You're assuming the user knows to put in two adjacent items from fibonacci sequence which is tricky to test.