Group number(从输入中读取一行字符串（最多80个字符），提取所有数字字符形成一个整数值，并输出原始数值及其双倍结果)

    #include<stdio.h>
    #include<string.h>
    #include<stdlib.h>
    int  shu(char a[]) {
    int sum = 0; int i, n = strlen(a); char b[80]; int flag = 0;
    for (i = 0; i < n; i++)
        if (a[i] <= '9' && a[i] >= 0)b[flag++] = a[i];
    b[flag] = '\0';
    sum = atoi(b);
    return sum;
    }
    int main() {
    printf("Enter a string:"); char a[80];
    gets_s(a);
    printf("digit=%d,%d", shu(a), 2 * shu(a));
    
    return 0;
    
    }