I can write a fib in C(i have a sample), but is there a more effective way like in Python, i get err-CodePudding

This gives first 15 of fibonacci sequence in C language, but I have to write each sequence manually, how do I make it increment the 2 variables instead of having endless amounts of variables? It was a lot easier in C and Python, not sure why I can't figure it out in C..

#include <stdio.h>
int i;
int main()
{

int var = 1;
int var1 = 1;

int var2 = var var1; 
printf("%d\n", var2);

int var3 = var2 var1;
printf("%d\n", var3);


int var4 = var3 var2; 
printf("%d\n", var4);

int var5 = var4 var3; 
printf("%d\n", var5);

int var6 = var5 var4; 
printf("%d\n", var6);


int var7 = var6 var5; 
printf("%d\n", var7);

int var8 = var7 var6; 
printf("%d\n", var8);

int var9 = var8 var7; 
printf("%d\n", var9);


int var10 = var9 var8; 
printf("%d\n", var10);

int var11 = var10 var9;
printf("%d\n", var11);

int var12 = var11 var10; 
printf("%d\n", var12);


int var13 = var12 var11;
printf("%d\n", var13);

int var14 = var13 var12; 
printf("%d\n", var14);

int var15 = var14 var13;
printf("%d\n", var15);


int var16 = var15 var14; 
printf("%d\n", var16);

int var17 = var16 var15;
printf("%d\n", var17);

int var18 = var17 var16; 
printf("%d\n", var18);


int var19 = var18 var17; 
printf("%d\n", var19);


}

Output: 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765

CodePudding user response：

Your question lacks key details. It's my guess that you are looking for something like Python's (x,y)=(y,x y).

>>> prev=3
>>> next=8
>>> (prev,next)=(next,prev next)
>>> prev
8
>>> next
11
>>>

Well,

(prev,next)=(next,prev next)

is basically equivalent to

tmp1 = next
tmp2 = prev next
prev = tmp1
next = tmp2

We can swap the last two assignments without breaking anything.

tmp1 = next
tmp2 = prev next
next = tmp2
prev = tmp1

This can be simplified.

this = next
next  = prev
prev = this

And that's exactly what you'd need to use here.

int n = 10;

if ( n > 0 ) {
   int prev = 0;
   printf( "%d\n", prev );

   int next = 1;
   for ( int i=1; i<n;   i ) {
      int this = next;
      printf( "%d\n", this );
      next  = prev;
      prev = this;
   }
}

Demo on Compiler Explorer

Note that we can fudge the starting values (1,0 instead of 0,1) to simplify the logic.

int n = 10;

int prev = 1;
int next = 0;

for ( int i=1; i<n;   i ) {
   int this = next;
   printf( "%d\n", this );

   next  = prev;
   prev = this;
}

Demo on Compiler Explorer

CodePudding user response：

Nevermind here it is, It just took me a while to figure it out, sorry.

#include <stdio.h>

int var = 1;

int var1 = 2;

int main()
{
while (var<100)
{
    var =var1;
    var1 = var;
printf("%d\n", var);
}

}