Question

I’m trying to solve the 3n+1 problem and I have a for loop that looks like this:

for(int i = low; i <= high; ++i)         {                 res = runalg(i);                 if (res > highestres)                 {                         highestres = res;                 }          } 

Unfortunately I’m getting this error when I try to compile with GCC:

3np1.c:15: error: ‘for’ loop initial declaration used outside C99 mode

I don’t know what C99 mode is. Any ideas?

Answer 1

I’d try to declare i outside of the loop!

Good luck on solving 3n+1 🙂

Here’s an example:

#include <stdio.h>  int main() {     int i;     /* for loop execution */    for (i = 10; i < 20; i++) {        printf('i: %d\n', i);    }        return 0; } 

Read more on for loops in C here.