字符串轉數字和數字轉字符串

字符串轉整數

字符串轉整數，不支持負號

int atoi(char s[])
{
    int n = 0;
    for (int i = 0; s[i] >= '0' && s[i] <= '9'; i++)
        n = 10*n + (s[i] - '0');
    return n;
}

整數轉字符串十進制，不支持負號

void itoa2(char s[],int n)
{   
    int i,tmp;
    for(i=0; n/10 != 0; n /= 10)
        s[i++] = n%10 + '0';
    s[i] = n + '0';
    s[i+1] = '\0';
    // reverse
    for(int j=0; j<i; ++j) {
        tmp = s[i];
        s[i--] = s[j];
        s[j] = tmp;
    }
}

整數轉字符串十進制，支持負號

void itoa(char s[],int n)
{   
    int i = 0,j=0,tmp;
    if(n < 0) {
        n = -n;
        s[i++] = '-';
        j = 1;
    }

    for(; n/10 != 0; n /= 10)
        s[i++] = n%10 + '0';
    s[i] = n + '0';
    s[i+1] = '\0';

    for( ; j<i; ++j) {
        tmp = s[i];
        s[i--] = s[j];
        s[j] = tmp;
    }
}