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


int main(){
    string n;
    cin>>n;
    string res="";
    if(n=="0"){//因为后面会忽略开头的0，所以前面要对0进行特判.这里注意不能写成=='0'
        cout<<0<<endl;
        return 0;
    }
    if(n[0]=='-'){
        res+='-';
    }
    bool isbegin=true;
    for(int i=n.length()-1;i>=0;i--){
        if(n[i]=='-'){
            continue;
        }
        if(isbegin&&n[i]=='0'){
            continue;
        }
        isbegin=false;
        res+=n[i];
    }
    cout<<res;
    return 0;
}

C :

#include<stdio.h>
int main()
{
	int a,b[20],l=0,s=0,i;
	scanf("%d",&a);
	for (i = 0;;++i)
	{
		l++;
		b[i]=a%10;
		a/=10;
		if(a==0)
			break;
		/* code */
	}
	for ( i = 0; i < l; ++i)
	{
		s=b[i]+s*10;
		/* code */
	}
	printf("%d",s );
	return 0;
}

C++ :

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main()
{
	char a[12];
	int i,count;
	while(scanf("%s",a)!=EOF)
	{
		if(atoi(a)==0)
		{
			printf("0\n");
			continue;
		}
		count=1;
		if(a[0]=='-')
		{
			printf("-");
			for(i=strlen(a)-1;i>=1;i--)
			{
				if(a[i]=='0'&&count==1)
				{
					continue;
				}
				if(a[i]!='0'||count==0)
				{
					count=0;
					printf("%c",a[i]);
				}
			}
		}
		else
		{
			for(i=strlen(a)-1;i>=0;i--)
			{
				if(a[i]=='0'&&count==1)
				{
					continue;
				}
				if(a[i]!='0'||count==0)
				{
					count=0;
					printf("%c",a[i]);
				}
			}
		}
		puts("");
	}
	return 0;
}

Pascal :

var
   s,s1,c:string;
   x,i,l:longint;
begin
 readln(s);
 if(s='0')then begin writeln(0);exit;end;
 if(s='-0')then begin writeln(0);exit;end;
 if s[1]='-'then
  begin
   c:='-';
   delete(s,1,1);
  end
 else c:='';
 l:=length(s);
 for i:=l downto 1 do
  begin
   s1:=s1+s[i];
  end;
 val(s1,x);
 str(x,s1);
 s1:=c+s1;
 writeln(s1);
end.

Java :

import java.util.Scanner;

public class Main {
public static void main(String[] args) {
	Scanner in = new Scanner(System.in);
	String a = in.next();
	if(Integer.parseInt(a)>0)
	{
		StringBuilder sb = new StringBuilder(a);
		sb.reverse();
		System.out.println(Integer.parseInt(sb.toString()));
	}
	else
	{
		char[] b = a.toCharArray();
		StringBuilder sb = new StringBuilder();
		for(int i=1;i<b.length;i++)
			sb.append(b[i]);
		sb.reverse();
		System.out.println(Integer.parseInt(sb.toString())*-1);
			
	}

}
}

Python :

# coding=utf-8
def main():
    def _reverse(x: int) -> int:
        sign = 1
        if x<0:
            sign = -1
            x = -x
        res = []
        while x>0:
            res.append(x%10)
            x //= 10
            
        x_ = 0
        for bit in res:
            if x_>2**31/10:
                return 0
            x_ = 10*x_ + bit 

        return sign*x_

    while True:
        temp = input()
        if temp == '':
            break
        x = int(temp)
        print(_reverse(x))

if __name__ == '__main__':
    main()