Interview Question: Convert a numeric string to an integer

#include<stdio.h>
#include<cctype>

int StrtoDecInt(const char* str){
    static const int MAX = (int)((unsigned)~0>>1);
    static const int MIN = -(int)((unsigned)~0 >> 1) - 1;

    unsigned int n = 0;
    int sign = 1;
    unsigned int c;

    while (isspace(*str))
        ++str;

    if( *str == '-' || *str == '+'){
        if(*str == '-')
            sign = -1;
        ++str;
    }

    while(isdigit(*str)){
        c=*str-'0';
        if(sign >0 && (n > MAX/10 || (n == MAX/10 && c > MAX % 10))){
            n = MAX;
            break;
        }else if (sign < 0 && (n > (unsigned) MIN/10 || (n== (unsigned) MIN/10 && c > (unsigned) MIN % 10))){
            n = MIN;
            break;
        }
        n = n*10 +c;
        ++str;
    }
    return sign > 0 ? n:-n;
}

int main(){
    const char* numstr="331";
    int num = StrtoDecInt(numstr);
    printf("number is : %d\n", num);
    return 0;
}