用户输入的C斐波那契

Question

Im trying to calculate the fibonacci sequence to a user input. So if the user inputs 10 the program will output all of the numbers in the sequence up to 10 in this case its 0, 1, 1, 2, 3, 5, 8

Here is my code:

#include <stdio.h>
int main ()
{
    /* variable definition: */
    int a, b, usrNumber;
    /* Initialize */
    a = 0;
    b = 1;
    usrNumber = 0;
    /* Ask user for number */
    printf("Please enter a positive number\n");
    scanf("%d", &usrNumber);
    /* Conduct Loop */
    while (b < usrNumber)
    {
        printf("%d \n",a);
        a += b;
        printf("%d \n",b);
        b += a;
    }
    return(0);
}

When I run it for 10, and 60 the sequence stops one number short then expected. When I run it for 90, or 300 the sequence works as expected. Any thoughts on why I can't get the lower numbers to work?

Answer 1

Change your loop to look like this:

while (a < usrNumber)
{
    printf("%d ", a);
    if (b < usrNumber) { 
        printf("%d ", b);
    }
    a = a + b;
    b = b + a;
}

If the user inputs 10, then by the end of the third time your loop runs, a is 8 and b is 13. So because b is larger then 10, the loop stops and a doesn't get printed even though it is smaller then 10

Answer 2

Instead of doing two steps per loop, you could use an auxiliar variable

while (b < usrNumber) { 
  aux=b;
  b+=a;
  a=aux;
  printf("%d ",b);} 

Answer 3

I haven't used C in a while so the following code might need to be changed a bit, but it seems to me that using a recursive function would make more sense for the Fibonacci Sequence:

    int GetFibonacciSequence(int index, bool printOutput)
    {
        int ret = 0;
        //Root of the function
        if (index == 0 || index == 1)
        {
            ret = index;
        }
        //Recursive portion
        else
        {
            int a = GetFibonacciSequence(index - 2, false);
            int b = GetFibonacciSequence(index - 1, printOutput);
            ret = (a + b);
        }
        //Output
        if (printOutput)
        {
            printf("%d ", ret);
        }
        return ret;
    }

Answer 4

Here's a quick and easy way to do it.

int main(){
    int a=0, c=1, b=1, sum=0, lim;
    scan("%d", &lim);
    while (C < lim){ printf("%d. ",c); c=a+b; a=b; b=c; }
    return 0;
}