C :

#include<stdio.h>
#include<string.h>

#define N 100


main()
{
	void add(char a[],char b[],char c[]);
	char a[N],b[N];
	char str[N];
	scanf("%s%s",a,b);
	add(a,b,str);
	printf("%s",str);
}

void add(char a[],char b[],char c[])
{
	int i,e,d;
	int n,m;
	char temp;
	n=strlen(a);
	m=strlen(b);
	for(i=0;i<n/2;i++) {temp=a[i];a[i]=a[n-1-i];a[n-1-i]=temp;}
	for(i=0;i<m/2;i++) {temp=b[i];b[i]=b[m-1-i];b[m-1-i]=temp;}

	e=0;
	for(i=0;i<n&&i<m;i++)
	{
		d=a[i]-'0'+b[i]-'0'+e;
		e=d/10;
		c[i]=d%10+'0';
	}
	if(i<m)
	{
		for(;i<m;i++)
		{
			d=b[i]-'0'+e;
			e=d/10;
			c[i]=d%10+'0';
		}
	}
	else
	{
		for(;i<n;i++)
		{
			d=a[i]-'0'+e;
			e=d/10;
			c[i]=d%10+'0';
		}
	}
	if(e) c[i++]=e+'0';
	c[i]=0;
	n=i;

	for(i=0;i<n/2;i++) {temp=c[i];c[i]=c[n-1-i];c[n-1-i]=temp;}
}

C++ :

#include<cstdio>
#include<cstring>
using namespace std;
struct node
{
    int len,a[110];
    node()
    {
        memset(a,0,sizeof(a));len=1;    
    }       
};

node pplus(node n1,node n2)
{
      node no;int i;
      if (n1.len>n2.len) no.len=n1.len;
      else no.len=n2.len;
      for (i=1;i<=no.len;i++) no.a[i]=n1.a[i]+n2.a[i];
       for (i=1;i<=no.len;i++)
       {
           no.a[i+1]+=no.a[i]/10;
           no.a[i]%=10;
       }i=no.len;
      while (no.a[i+1]>0)
      {
         i++;
         no.a[i+1]=no.a[i]/10;
         no.a[i]%=10;
       }no.len=i;
      return no;
}

char s1[110],s2[110];

int main()
{
   node n1,n2,no;int i;
   scanf("%s",s1);
   scanf("%s",s2);
   n1.len=strlen(s1);n2.len=strlen(s2);
   for(i=0;i<n1.len;i++)
       n1.a[i+1]=s1[n1.len-i-1]-'0';
   for(i=0;i<n2.len;i++)
       n2.a[i+1]=s2[n2.len-i-1]-'0';
   no=pplus(n1,n2);
   for(i=no.len;i>=1;i--)
     printf("%d",no.a[i]);
   printf("\n");  
   return 0;
}

Java :

import java.util.Scanner;



public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
Scanner in = new Scanner(System.in);

String a = in.next();
String b = in.next();
plus p = new plus();
p.pl(a, b);
	}

}
class plus {
	String str = "";

	public void pl(String a, String b) {
		int lenA = a.length();
		int lenB = b.length();
		int max = (lenA >= lenB) ? lenA : lenB;
		int min = (lenB > lenA )? lenA : lenB;
		String zr = "0";

		for (int i = 0; i < max - min; i++) {
			str += zr ;
		}
		if (max == lenA) {
			b = str+b;
			
		} else {
			a = str +a;
		}

		int jw = 0;
		String haha = "";
		for (int j = max - 1; j >= 0; j--) {
			int s=0;
			
			int tA = Integer.parseInt(String.valueOf(a.charAt(j)));
			int tB = Integer.parseInt(String.valueOf(b.charAt(j)));
			if (tA + tB + jw >= 10) {
				if(j==0){
					s += tA + tB +jw;
					jw = 1;
				}else{
					s += tA + tB +jw- 10;
				jw = 1;
				}
				
			} else {
				s += tA + tB+jw;
				jw = 0;
			}
			
			
			
////			str += String.valueOf(s) + str;
//			System.out.print(String.valueOf(s));
			haha =String.valueOf(s)+haha;
			
		}
		System.out.println(haha);
	}
}