Precision Calculation-big number multiplied by large number, precision calculation by large number

Precision Calculation-big number multiplied by large number, precision calculation by large number
The algorithm is used to calculate a large number (a number that cannot be expressed by an existing data type) multiplied by a large number (a number that cannot be expressed by an existing data type ). The algorithm is to put every bit of a large number as a character into a character array, and then multiply each bit of the multiplier and each bit of the multiplier from the highest bit, store the result in a two-dimensional array res. For example, 12*12, res [0] [0] = 1, res [0] [1] = 2, res [1] [0] = 2, res [1] [1] = 4, then the final result array s, s [0] = res [0] [0] = 1, s [1] = res [0] [1] + res [1] [0] = 4, s [2] = res [1] [1] = 4, however, if the output is 441, we need to use the for loop to reverse the result. The Calculation of more digits will be more troublesome in the process, but it is the same as the calculation of more digits.

#include<stdio.h>#include<string.h>void mult(char a[],char b[],char s[]);main(){char a[65] = "12";char b[65] = "12";char s[130] = "";mult(a,b,s);printf("%s",s);}void mult(char a[],char b[],char s[]){int i,j,k=0,alen,blen,sum=0,res[65][65]={0},flag=0;char result[65];alen=strlen(a);blen=strlen(b); for (i=0;i<alen;i++){for (j=0;j<blen;j++){res[i][j]=(a[i]-'0')*(b[j]-'0');}}for (i=alen-1;i>=0;i--){for (j=blen-1;j>=0;j--){sum=sum+res[i+blen-j-1][j];}result[k]=sum%10;k=k+1;sum=sum/10;}for (i=blen-2;i>=0;i--){for (j=0;j<=i;j++){sum=sum+res[i-j][j];}result[k]=sum%10;k=k+1;sum=sum/10;}if (sum!=0) {result[k]=sum;k=k+1;}for (i=0;i<k;i++) {result[i]+='0';}for (i=k-1;i>=0;i--) {s[i]=result[k-1-i];}s[k]='\0';while(1){if (strlen(s)!=strlen(a)&&s[0]=='0') strcpy(s,s+1);elsebreak;}}

Below is the implementation process of my C language.