第四阶段—数组—字符数组和字符串—字符数组：把字符串“123456”转换成数值 123456

#include <stdlib.h>
#include <stdio.h>
#define N 32
int my_atoi(char *s);
int main()
{
    char a[N];
    scanf("%s", a);
    int num = 0;
    num = my_atoi(a);
    printf("%d\n", num);
    return 0;
}
int my_atoi(char *s)
{
    char *p = s;
    char c;
    int i = 0;
    while(c=*p++)
    {
        if(c>='0' && c<='9')
        {
            //i = i*10 + (c-'0');
            i = c-'0';
        }
        else
        return -1; 
    }
        return i;
}