C + + Converts a string type to int, float, and double type mainly in the following ways:

C + + Converts a string type to int, float, and double type mainly in the following ways:

# method One: Use StringStream

StringStream has been introduced in methods that convert int or float types to string types, and can also be used as a type of string to convert to a commonly used numeric type.

Demo:

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2. #include <iostream>
4. #include <sstream>//use StringStream to introduce this header file
6. Using namespace std;
10. Template functions: Converting a string variable to a common numeric type (this method is universally applicable)
12. Template <class type>
14. Type stringtonum (const string& str)
16. {
18. Istringstream ISS (str);
20. Type num;
22. ISS >> num;
24. return num;
26. }
30. int main (int argc, char* argv[])
32. {
34. String str ("00801");
36. cout << stringtonum<int> (str) << Endl;
40. System ("pause");
42. return 0;
44. }

Output Result:

801 Please press any key to continue ...

#方法二: Use the Atoi (), Atil (), atof () functions-----------------are actually conversions of char types to numeric types

Note : If string s is empty with Atoi, the return value is 0. It is not possible to determine if s is 0 or null

1. Atoi (): int atoi (const char * str);

Description: Parses the C string str interpreting its content as a integral number, which is returned as an int valu E.

parameter: str : C string beginning with the representation of a integral number.

return value: 1.  The successful conversion displays a value of type int.  2. the non-convertible string returns 0. 3. if the buffer overflows after the conversion, return Int_max orint_min

Demo:

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2. #include <iostream>
4. Using namespace std;
6. int main ()
8. {
10. int i;
12. char szinput [256];
14. cout<<"Enter a number:" <<endl;
16. Fgets (Szinput, stdin);
18. i = atoi (szinput);
20. cout<<"The value entered is:" <<szInput<<endl;
22. cout<<"The number convert is:" <<i<<endl;
24. return 0;
26. }

Output:

Enter a number:48 The value entered is:48 The number convert is:48

2.aotl (): Long int atol (const char * str);

Description: C string str interpreting its content as an integral number, which is returned as a long int value (usage and at Oi function similar, return value is long int)

3.atof (): Double atof (const char * str);

Parameters: C string beginning with the representation of a floating-point number.

return Value:  1. Conversion successfully returns a value of type Doublel 2. Cannot convert, return 0.0. 3. Cross-border, return to huge_val

Demo:

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2. /* Atof example:sine Calculator */
4. #include <stdio.h>
6. #include <stdlib.h>
8. #include <math.h>
10. int main ()
12. {
14. double n,m;
16. double pi=3.1415926535;
18. char szinput [256];
20. printf ( "Enter degrees:");
22. Gets (Szinput);
24. convert//char type to double type
26. n = atof (szinput);
28. m = sin (n*pi/180);
30. printf ( "The sine of%f degrees is%f\n", N, m);
34. return 0;
36. }

C + + Converts a string type to int, float, and double type mainly in the following ways: