“123”——> 123

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;

int main()
{

    char num[110];
    scanf("%s",num);
    int len = strlen(num);
    int t=1,tmp=0;
    for(int i=len-1;i>=0;i--)
    {
        tmp = tmp + (num[i]-'0')*t;
        t = t*10;
    }
    printf("%d\n",tmp);
    return 0;
}

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;

int main()
{

    char num[110];
    scanf("%s",num);
    int len = strlen(num);
    int tmp = 0;
    for(int i=0;i<len;i++)
    {
        tmp = 10*tmp + num[i]-'0';
    }
    printf("%d\n",tmp);
    return 0;
}