Write a program in C language for addition of two numbers which have at least 20 digits each

#include<stdio.h>#include<conio.h>#include<string.h>void main(){char str1[21],str2[21];int i,j,a[20],b[20];int add[21]={0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
printf("n Enter number 1:"); for(i=0; i<21; i++) { str1[i]=getchar(); } printf("n Enter number 2:"); for(i=0; i<21; i++) { str2[i]=getchar(); }
//converting char to integer for(i=0; i<20; i++) { a[i]=(int)str1[i]-48; b[i]=(int)str2[i]-48; } printf("n Print Number 1:"); for(i=0; i<20; i++) { printf("%d",a[i]); } printf("n Print Number 2:"); for(i=0; i<20; i++) { printf("%d",b[i]); } for(i=20; i>-1;i–) { j= a[i]+b[i]; if(j<10) { add[i] +=j; } else { add[i]+=(j-10); add[i-1]+=1; } } printf("n Print Addition:"); for(i=0; i<20; i++) { printf("%d",add[i]); }   getch();}