为啥第一个点错了？求助

漠怀 @ 2019-12-15 12:56:43

#include<bits/stdc++.h>
using namespace std;
int a[2100];
int b[2100];
int c[4100000] = {0};
void read(int *p)
{
    char ch = getchar();
    while (ch < '0'||ch > '9') ch = getchar();
    p[1] = ch - '0';
    p[0] = 1;
    ch = getchar();
    while (ch >= '0'&&ch <= '9')
    {
        p[++p[0]] = ch - '0';
        ch = getchar();
    }
    for (int i = 1;i <= p[0] / 2;i++)
    {
        int t = p[i];
        p[i] = p[p[0] - i + 1];
        p[p[0] - i + 1] = t;
    }
}

void ab_mult(int const *a,int const *b,int *c)
{
    c[0] = a[0] + b[0] - 1;
    for (int i = 1;i <= a[0];i++)
        for (int j = 1;j <= b[0];j++)
            c[i+j-1] += a[i] * b[j];
    for (int i = 1;i <= c[0];i++)
    {
        c[i+1] += c[i]/10;
        c[i] %= 10;
    }
    while (c[c[0]+1])
    {
        c[0]++;
        c[c[0]+1] += c[c[0]]/10;
        c[c[0]] %= 10;
    }
}

int main()
{
    read(a);
    read(b);
    ab_mult(a,b,c);
    for (int i = c[0];i >= 1;i--) cout<<c[i];
    return 0;
}

by 金苹果gold @ 2019-12-15 22:47:03

答案是零，就输不出来

by Monkey_Hunter @ 2020-01-22 18:42:25

#include<bits/stdc++.h>
using namespace std;
int a[2100];
int b[2100];
int c[4100000] = {0};
void read(int *p)
{
    char ch = getchar();
    while (ch < '0'||ch > '9') ch = getchar();
    p[1] = ch - '0';
    p[0] = 1;
    ch = getchar();
    while (ch >= '0'&&ch <= '9')
    {
        p[++p[0]] = ch - '0';
        ch = getchar();
    }
    for (int i = 1;i <= p[0] / 2;i++)
    {
        int t = p[i];
        p[i] = p[p[0] - i + 1];
        p[p[0] - i + 1] = t;
    }
}

void ab_mult(int const *a,int const *b,int *c)
{
    c[0] = a[0] + b[0] - 1;
    for (int i = 1;i <= a[0];i++)
        for (int j = 1;j <= b[0];j++)
            c[i+j-1] += a[i] * b[j];
    for (int i = 1;i <= c[0];i++)
    {
        c[i+1] += c[i]/10;
        c[i] %= 10;
    }
    while (c[c[0]+1])
    {
        c[0]++;
        c[c[0]+1] += c[c[0]]/10;
        c[c[0]] %= 10;
    }
}

int main()
{
    read(a);
    read(b);
    ab_mult(a,b,c);
    for (int i = c[0];i >= 1/*这里改成i>1*/;i--) cout<<c[i];
    return 0;
}