ぼるじょあがC/C++の宿題を片づけますYO! 67代目

>811
メインは省略
double suma(int n) {
int i;
double sum = 0;
for(i=1; i<=n; i++) {
  if(i%2) sum += (double)1 / i;
  else sum -= (double)1 / i; }
return sum;
}
double sumb(int n) {
int i;
double sum = 0;
for(i=n; i > 0; i--) {
  if(i%2) sum += (double)1 / i;
  else sum -= (double)1 / i; }
return sum;
}
double sumc(int n) {
int i;
double sum = 0;
for(i=1; i<=n; i+=2) sum += (double)1 / i;
for(i=2; i<=n; i+=2) sum -= (double)1 / i;
return sum;
}
double sumd(int n) {
int i;
double sum = 0;
for(i=n; i > 0; i-=2) sum += (double)1 / i;
for(i=n-1; i > 0; i-=2) sum -=(double)1 / i;
return n % 2 ? sum : -sum;
}