大数运算

下面这段程序包含了大数的加、减、乘运算的代码，除法运算尚在研究中。

/* * ===================================================================================== * * Filename: LargeNumOp.c * * Description: The regular version of Large Number Multiplication. * * Version: 1.0 * Created: 08/23/2009 07:02:48 PM * Revision: none * Compiler: gcc * * Author: Bonn Yang * Company: * * ===================================================================================== */ #include <stdio.h> #include <string.h> /* * Large number multiplication. * a*b=c * The product stores in c. */ void multiply(char* a,char* b,char* c) { int i,j,ca,cb,* s; ca=strlen(a); cb=strlen(b); s=(int*)malloc(sizeof(int)*(ca+cb)); for (i=0;i<ca+cb;i++) s[i]=0; for (i=0;i<ca;i++) for (j=0;j<cb;j++) s[i+j+1]+=(a[i]-'0')*(b[j]-'0'); for (i=ca+cb-1;i>=0;i--) if (s[i]>=10) { s[i-1]+=s[i]/10; s[i]%=10; } i=0; while (s[i]==0) i++; for (j=0;i<ca+cb;i++,j++) c[j]=s[i]+'0'; c[j]='/0'; free(s); } /* Large number addition * a+b=c */ void add(char* a, char* b, char* c) { int i,j,ca,cb,rlen,* s; ca=strlen(a); cb=strlen(b); rlen=((ca>cb)?ca:cb)+1; /* len of result */ s=(int*)malloc(sizeof(int)*rlen); for (i=0;i<rlen;i++) s[i]=0; if(ca>cb) { for(i=0;i<ca-cb;i++) s[i+1]=a[i]-'0'; for(i=ca-cb;i<ca;i++) s[i+1]=(a[i]-'0')+(b[i-ca+cb]-'0'); } else { for(i=0;i<cb-ca;i++) s[i+1]=b[i]-'0'; for(i=cb-ca;i<cb;i++) s[i+1]=(a[i-cb+ca]-'0')+(b[i]-'0'); } for (i=rlen-1;i>=0;i--) if (s[i]>=10) { s[i-1]+=s[i]/10; s[i]%=10; } i=0; while (s[i]==0) i++; for (j=0;i<rlen;i++,j++) c[j]=s[i]+'0'; c[j]='/0'; free(s); } /* Large number substraction * a-b=c */ void sub(char* a,char* b,char* c) { int i,j,ca,cb,rlen,* s; ca=strlen(a); cb=strlen(b); rlen=((ca>cb)?ca:cb)+1; /* len of result, the first byte is negative or positive sign */ s=(int*)malloc(sizeof(int)*rlen); for (i=0;i<rlen;i++) s[i]=0; if(ca>cb) { s[0]='+'; for(i=ca-1;i>=ca-cb;i--) { if(a[i]>b[i-ca+cb]) { s[i+1]=(a[i]-'0')-(b[i-ca+cb]-'0'); } else if(a[i]<b[i-ca+cb]) { s[i+1]=(a[i]-'0'+10)-(b[i-ca+cb]-'0'); a[i-1]-=1; } else s[i+1]=0; } for(i=ca-cb-1;i>=1;i--) { if(a[i]>0) { s[i+1]=(a[i]-'0'); } else if(a[i]<0) { s[i+1]=a[i]-'0'+10; a[i-1]-=1; } else s[i+1]=0; } s[1]=a[i]-'0'; } else if(ca<cb) { s[0]='-'; for(i=cb-1;i>cb-ca-1;i--) { if(b[i]>a[i-cb+ca]) { s[i+1]=(b[i]-'0')-(a[i-cb+ca]-'0'); } else if(b[i]<a[i-ca+cb]) { s[i+1]=(b[i]-'0'+10)-(a[i-cb+ca]-'0'); b[i-1]-=1; } else s[i+1]=0; } for(i=cb-ca-1;i>=1;i--) { if(b[i]>0) { s[i+1]=(b[i]-'0'); } else if(b[i]<0) { s[i+1]=b[i]-'0'+10; b[i-1]-=1; } else s[i+1]=0; } s[1]=b[i]-'0'; } else /* ca==cb */ { if(strcmp(a,b)>0) /* a>b */ { s[0]='+'; for(i=ca-1;i>=1;i--) { if(a[i]>b[i]) { s[i+1]=(a[i]-'0')-(b[i]-'0'); } else if(a[i]<b[i]) { s[i+1]=(a[i]-'0'+10)-(b[i]-'0'); a[i-1]-=1; } else s[i+1]=0; } s[1]=(a[i]-'0')-(b[i]-'0'); } else if(strcmp(a,b)<0) /* a<b */ { s[0]='-'; for(i=ca-1;i>=1;--i) { if(b[i]>a[i]) { s[i+1]=(b[i]-'0')-(a[i]-'0'); } else if(b[i]<a[i]) { s[i+1]=(b[i]-'0'+10)-(a[i]-'0'); b[i-1]-=1; } else s[i+1]=0; } s[1]=(b[i]-'0')-(a[i]-'0'); } else /* a==b */ { c[0]='+'; c[1]='0'; c[2]='/0'; free(s); } } c[0]=s[0]; i=1;j=1; while ((s[i]==0) && (i<rlen)) i++; if(i!=rlen) /* result is not zero */ { for (j=1;i<rlen;i++,j++) { if(s[i]<0) c[j]='0'-s[i]; else c[j]=s[i]+'0'; } } else { /* result is zero */ c[j++]='0'; } c[j]='/0'; free(s); } int main() { char a[1024]={'/0'}; char b[1024]={'/0'}; char c[1024]={'/0'}; printf("Enter two numbers:/n"); gets(a); gets(b); multiply(a,b,c); printf("%s * %s = %s/n",a,b,c); add(a,b,c); printf("%s + %s = %s/n",a,b,c); sub(a,b,c); printf("%s - %s = %s/n",a,b,c); return 0; }