C ++如何将字符串转换为char数组并检查数字？

Question

how do I do this? i want it to check for numbers

cout<<"Enter your first number: ";
std::cin >> dblNumOne;
int i=0;
char str[]=dblNumkOne;
while (str[i])
{
    if (isalpha(str[i])) printf ("character %c is alphabetic\n",str[i]);
    else printf ("character %c is not alphabetic\n",str[i]);
    i++;
}

Answer 1

Simple, just iterate through the std::string as such:

std::string dblNumOne;
std::cin >> dblNumOne;

for(unsigned int i = 0; i < dblNumOne.length(); i++)
{
    if (isalpha(dblNumOne[i]))
    {
        printf ("character %c is alphabetic\n", dblNumOne[i]);
    }
    else
    {
        printf ("character %c is not alphabetic\n", dblNumOne[i]);
    }
}

Answer 2

One way is to use string instead of char, because string has a length function

so like this:

std::string dblNumOne;
std::cout<<"Enter your first number: ";
std::cin >> dblNumOne;
std::cout << dblNumOne.length() << endl;

If you have to use char, then you can simply do it by checking '\\0' value which stands for end of string.

My approach would be use the string and get the length of it and then convert it to char array by using c_str() function.

Answer 3

1) Convert the string to a char array:

strcpy(charArray,stringArray.c_str());

Source: http://v2.cplusplus.com/forum/windows/71633/

2) Print out whether it's a digit or not using isdigit :

while (charArray[i]) {
    if (isdigit(charArray[i])){
        printf ("character %c is a digit\n",str[i]);
    } else {
        printf ("character %c is not a digit\n",str[i]);
    }
    i++;
}

Remember to click the grey check mark (the ✓) to the left of my answer if it answers your question or led you to the answer!

Answer 4

If you want to check for numbers, you could try this:

std::string str = "";
std::cout<<"enter string>>";
std::cin>>str;

int is_number = 0; 
char filter[] = "0123456789";

for(int n=0; n<str.size(); ++n){
   for(int i=0; i<10; ++i){

      if(str[n] == filter[i]){
          ++is_number;
          break; // found match, filter next char in str
      }else if(str[n] != filter[i] && i == 9){
          std::cout<<"'"<<str[n]<<"' is not a digit!\n";
      }
   }
}

if(is_number == str.size()){
    std::cout<<"You entered a number";
}else std::cout<<"You didn't enter a number!";

or to recognize decimal numbers you could try this:

int is_number = 0, is_decimal = 0; 
char filter[] = ".0123456789";

for(int n=0; n<str.size(); ++n){
   for(int i=0; i<11; ++i){

      if(str[n] == filter[i]){
          if(filter[i] == '.'){
            ++is_decimal;
          }
          ++is_number;
          break;
      }
   }
}// for decimal

if(is_number == str.size() && is_decimal <= 1){
    std::cout<<"You entered a number";
}else std::cout<<"You didn't enter a number!";