用for循环该怎么写，希望得到指导

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
float polynomial(int n){
     float sum=0;
     int i;
     for(i=1;i<=n;i++){
         if(i%2 == 1)
             sum += 1.0/i;
         if(i%2 == 0)
             sum -= 1.0/i;
     }
     return sum;

}
int main(int argc,char *argv[]) {
    int t=100;
    float sum;
    sum = polynomial(t);
    printf("sum=%.5f\n",sum);
    return EXIT_SUCCESS;
}

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
{
    double sum=0.0;
    int n=0;
    scanf("%d",&n);
    
    while(n)
    {
        if(n%2)
            sum-=1.0/n;
        else
            sum+=1.0/n;
        --n;
    }
    printf("%.5lf",sum);
}