我死在50分上了

#include<bits/stdc++.h>
#define N 100001
using namespace std;
int a[501],b[501],c[501];
char a1[501],b1[501];
void convert(char s[],int a[])
{
reverse(s,s+strlen(s));
for(int i=0;i<strlen(s);i++)a[i]=s[i]-48;
}
int cheng(int a[],int b[],int lena,int lenb)    
{
int x=0,i,j;
for(i=0;i<lenb;i++)
{
x=0;
for(j=0;j<lena;j++)
{
c[i+j]=c[i+j]+a[j]*b[i]+x;
x=c[i+j]/10;
c[i+j]=c[i+j]%10;
}
c[i+j]=x;
}
if(x)
{
c[i+j-1]=x;
return i+j-1;
}
else
return i+j-2;
}
void print(int a[],int len)
{
while(a[len]==0)len--;
if(len<0)
cout<<0;
else
for(int i=len;i>=0;i--)cout<<a[i];
}
int main()
{
int i,j,k,len,w;
cin>>a1;
cin>>b1;
convert(a1,a);
convert(b1,b);
len=cheng(a,b,strlen(a1),strlen(b1));
print(c,len);
return 0;
}

#include <iostream>

using namespace std;
const int N=201;
string s1,s2;
int a1[N],a2[2*N],a3[N],a4[N],i,j,k,t;
int main()
{
cin>>s1>>s2;
int l1=s1.size(),l2=s2.size();
for(i=0;i<l1;i++)a3[l1-i-1]=s1[i]-'0';
for(i=0;i<l2;i++)a4[l2-i-1]=s2[i]-'0';
for(i=0;i<l2;i++){
for(j=0,k=i;j<l1;j++){
t=a1[k+j]+a3[j]*a4[i];
a1[k+j]=t%10;
a1[k+j+1]=t/10;
}
for(k=i;k<=i+l1;k++){
t=a2[k]+a1[k];
a2[k]=t%10;
a2[k+1]+=t/10;
a1[k]=0;
}
}
for(k=l1+l2-1;a2[k]==0&&k>=0;k--);
if(k<0)cout<<0;
while(k>=0) cout<<a2[k--];
return 0;
}

#include<bits/stdc++.h>
using namespace std;

char s[500];
int a[500], b[500], c[5000];
void read(int bn[])
{   
scanf("%s", s);
int len = strlen(s);
bn[0] = len;
for (int i = 1; i <= len; i++)
bn[i] = s[len-i] - '0';
}
void mul(int a[], int 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];
c[i+j] += c[i+j-1] / 10;
c[i+j-1] %= 10;
}
if (c[c[0] + 1]) c[0]++;
}

int main()
{
read(a);
read(b);
mul(a, b, c);
while(c[c[0]] == 0 && c[0] > 1) c[0]--;
for(int i = c[0]; i > 0; i--)
printf("%d", c[i]);
return 0;
}