This question already has answers here:
Cannot implicitly convert type 'int' to 'string'
(4 answers)
Closed 2 years ago.
As someone who's only ever used c++, i'm so confused. I've gone over different explanations but i still can't seem to understand it. Why do i, for example, need to check if a string is a string? (the tryparse method) If it's a number obviously its an int...right?? So for example my current code takes in age in one function and outputs it in the main function. I tried converting it to int but i got error cs0019: Operator '==' cannot be applied to operands of 'int' and 'string'
public static string GetAge()
{
Console.WriteLine("\nPlease input age > ");
int age = Int32.Parse(Console.ReadLine());
if (age == "")
{
do {
Console.Write("Invalid input. Please try again > ");
age = Console.ReadLine();
} while ( age == "");
}
return age;
}
static void Main (){
Console.WriteLine("\nPlease note\nThis program is only applicable for users born between 1999 and 2010");
string name = GetName();
string year = GetYear();
int age = GetAge();
And then i also get this error cs0029:Cannot implicitly convert type 'int' to 'string' (line 49 which is return age) and error cs0029: cannot implicitly convert type 'string' to 'int' for line 58 (int age =GetAge();)
int.Parse will throw an exception if it fails. I would modify your loop to this:
int age;
while (!int.TryParse(Console.ReadLine(), out age))
Console.Write("Invalid input. Please try again > ");
return age;
int.TryParse will return true upon success.
Also change the method definition to return an int instead:
public static int GetAge()
I don't understand what do you want and why. :-)
You don't need to check string is string.
int.Parse will throwing an exception, when the input is not a valid integer, but you can use TryParse, what is returns a boolean and does not throw exception.
In C# you can't compare integers and strings, you must convert it first.
Your GetAge method returns integer, but the return type declared as string.
public static int GetAge()
{
int age;
Console.Write("\nPlease input age > ");
while (!int.TryParse(Console.ReadLine(), out int age))
{
Console.Write("Invalid input. Please try again > ");
};
return age;
}
static void Main()
{
Console.WriteLine("\nPlease note\nThis program is only applicable for users born between 1999 and 2010");
string name = GetName();
string year = GetYear();
int age = GetAge();
}
Related
This question already has answers here:
How can I convert String to Int?
(31 answers)
Closed 3 months ago.
I want to add two numbers using Console.ReadLine(), but it gives me the error
Invalid expression term 'int'
Here is my code:
using System;
namespace MyApplication
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Enter a number:");
string number1 = Console.ReadLine();
Console.WriteLine("Enter another number:");
string number2 = Console.ReadLine();
Console.WriteLine("The sum of those numbers is:");
Console.WriteLine(int(number1) + int(number2));
}
}
}
Could you help?
Use the Convert.ToInt32() method to convert from string to int.
Console.WriteLine(Convert.ToInt32(number1) + Convert.ToInt32(number2));
See How can I convert String to Int? for more examples or alternatives.
Note: You write
string s = "42";
int i = int(s); // Compiler error Invalid Expression term
This syntax is used for type casting in languages like Pascal or Python. But in C based languages like C#, C++ or Java you use a different syntax:
string s = "42";
int i = (int)s; // Compiler error invalid cast
Round brackets around the type name, not around the value. This will still not work, though, because there is no direct cast from type string to type int in C#. It would work for different types:
double d = 42d;
int i = (int)d; // Works
I am trying to convert a string variable to a double.
So far I have tried Convert.ToDouble()
string userAge;
Console.WriteLine("What is your age?");
Console.ReadLine();
Convert.ToDouble(userAge);
and when I tried to do operations on userAge it shows this error:
Program.cs(23,27): error CS0019: Operator '/' cannot be applied to operands of type 'string' and 'double' [/home/ccuser/workspace/csharp-working-with-numbers-arithmetic-operators-csharp/e3-workspace.csproj]
Program.cs(29,28): error CS0029: Cannot implicitly convert type 'string' to 'double' [/home/ccuser/workspace/csharp-working-with-numbers-arithmetic-operators-csharp/e3-workspace.csproj]
Program.cs(17,24): error CS0165: Use of unassigned local variable 'userAge' [/home/ccuser/workspace/csharp-working-with-numbers-arithmetic-operators-csharp/e3-workspace.csproj]
The build failed. Fix the build errors and run again.
Any suggestions?
To begin with, you need to assign the result of those method calls (to get the user input and then convert the string to a doulbe) to some variables so you can use them later in the code:
Console.WriteLine("What is your age?");
string input = Console.ReadLine();
double age = Convert.ToDouble(input);
But now we see there is a problem - if the user enters a non-numeric input, we'll get a FormatException.
Luckily there's a better method we can use for parsing strings to doubles: double.TryParse. This method takes in a string (the input), and an out parameter that it will set to the converted value on success (or the default value of 0 on failure). And the best thing is that it returns a bool that indicates if it was successful or not, so we can use it as a condition for a loop:
Console.Write("What is your age? ");
string userAge = Console.ReadLine();
double age;
while (!double.TryParse(userAge, out age))
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Invalid input, please try again.");
Console.ResetColor();
Console.Write("What is your age? ");
userAge = Console.ReadLine();
}
// Now 'age' is the converted value entered by the user
Now we have a solution that will loop until the user enters a valid number. But that's a fair amount of code. What if we have to get another number from them? Probably it would be better to extract this into a method that takes in a string (to use as a prompt) and which returns the strongly-typed double result:
public static double GetDoubleFromUser(string prompt)
{
bool isValid = true;
double result;
do
{
if (!isValid)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Invalid input, please try again.");
Console.ResetColor();
}
else isValid = false;
Console.Write(prompt);
} while (!double.TryParse(Console.ReadLine(), out result));
return result;
}
Now our main code is much more simple:
double userAge = GetDoubleFromUser("What is your age? ");
double userWeight = GetDoubleFromUser("What is your weight? ");
Now, if we want to get a little fancier, we can include an optional 'validator' argument, which is a function that takes in a double and returns a bool, which we can use to further validate the result and force the user to enter a valid number.
For example, what if we want them to choose a number from 1 to 10? We don't want to have to setup a loop again for this further validation, so let's pass a Func<double, bool> to the method so it can do the validation for us!
For example:
public static double GetDoubleFromUser(string prompt, Func<double, bool> validator = null)
{
bool isValid = true;
double result;
do
{
if (!isValid)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Invalid input, please try again.");
Console.ResetColor();
}
else isValid = false;
Console.Write(prompt);
} while (!double.TryParse(Console.ReadLine(), out result) &&
(validator == null || !validator.Invoke(result)));
return result;
}
Now we can pass in whatever validation we want to do on the input to the method! This would look something like the line of code below, and the method will not return until the user enters a valid number that's greater than or equal to 1 and less than or equal to 10:
double number = GetDoubleFromUser("Choose a number from 1 to 10: ",
x => x >= 1 && x <= 10);
You aren't assigning the result of your Convert call to a variable, you're just throwing it away. Convert doesn't alter the type of the existing variable (because, apart from other considerations, you simply can't do that in a strongly-typed language), instead it produces a new variable for you to use in your maths.
The error is, I presume without seeing the relevant code, because you tried to use userAge in your calculations which, as I've just explained, is still a string.
Also, to go back a step, you've never actually assigned the result of the ReadLine operation to the userAge variable in the first place.
This:
Console.WriteLine("What is your age?");
string userAge = Console.ReadLine();
double age = Convert.ToDouble(userAge);
would make more sense. And then use age in your calculations afterwards.
So this is my code
static void Main(string[] args)
{
Program.AgeAndLabel();
}
public static string AgeAndLabel(string userAge)
{
Console.WriteLine("Enter your age.");
int ageValue = int.Parse(Console.ReadLine());
if (ageValue < 18)
userAge = "Minor";
else
userAge = "Adult";
return userAge;
}
For Program.AgeAndLabel, I am getting the error "There is no argument given that corresponds to the required formal parameter'userAge' of 'Program.AgeAndLabel(string)'" and I don't understand why. I am new to this website and coding in general so if you have any constructive criticism let me know.
Remove the string userAge from the function arguments and add it inside function instead; that is where it is needed. The issue is that the variable does not exist inside the function scope where you assign to it.
Also, you are calling the function without arguments, which implies you meant the function to have no arguments.
Your function should probably look something like this:
public static string AgeAndLabel()
{
string userAge;
Console.WriteLine("Enter your age.");
int ageValue = int.Parse(Console.ReadLine());
if (ageValue < 18)
userAge = "Minor";
else
userAge = "Adult";
return userAge;
}
If you had used the ternary operator the last five lines could have been reduced to this instead:
return (ageValue < 18) ? "Minor" : "Adult";
but it's just another (shorter) way of expressing the same thing. (Although less code (usually) means less risk of errors)
This question already has answers here:
Cannot implicitly convert type string to int
(4 answers)
Closed 8 years ago.
I'm on my way to learn C# by following the basic training tutorial from Lynda and trying to make some changes on their examples.
I'm stuck on an error that I can't find a solution for on Google.
Cannot implicitly convert type 'string' to 'int' (CS0029)
Code:
namespace l2
{
class Program
{
public static void Main(string[] args)
{
int arg;
arg = Console.ReadLine();
int result1;
result1 = formula(arg);
Console.WriteLine("the result is {0}",result1);
Console.ReadKey();
}
static int formula (int theVal){
return (theVal * 2 + 15);
}
}
}
I really don't understand why I get that error. My function is getting an int, the arg that I want to get from console is also an int. Where is the string that the compiler is talking about? :)
Console.ReadLine() returns a string.
What you want is
arg = int.Parse(Console.ReadLine());
The correct solution in this case will be.
string input;
input= Console.ReadLine();
int numberArg;
while (!int.TryParse(input, out numberArg))
{
Console.WriteLine(#"Wrong parameter. Type again.");
input= Console.ReadLine();
}
var result1 = formula(numberArg);
Console.WriteLine("the result is {0}", result1);
Console.ReadKey();
You could also attempt some subtle validation, by using the int.TryParse. Which will attempt to convert the value to an integer, if it indeed fails it will use the original value:
int id = 1;
int.TryParse("Hello", out id);
Console.WriteLine(id)
Output: 1
int id = 1;
int.TryParse("40", out id);
Console.WriteLine(id)
Output: 40
Also note that Console.ReadLine() will return a type of string. So to correctly solve your issue, you would do:
int arguement = 0;
while(!int.TryParse(Console.ReadLine(), out arguement)
{
Console.WriteLine(#"Error, invalid integer.");
Console.ReadLine();
}
So until they enter a valid integer they'll be trapped in the loop.
This question already has answers here:
How can I convert String to Int?
(31 answers)
Cannot implicitly convert type 'string' to 'int' error
(3 answers)
Closed 8 years ago.
I'm trying to write a program, and I want the program to read a line.
it is giving me this error
Cannot implicitly convert type 'string' to 'int
How can I convert the string to int? This is the part of the program that's giving the error.
class engineering : faculty
{
public engineering() \\constructor
{
}
public int maths_grade;
public override void fill_form()
{
Console.WriteLine("Insert Maths Grades: ");
int maths_grade = Console.ReadLine();
}
}
Try
int mathsGrade;
if (int.TryParse(Console.ReadLine(), out mathsGrade))
{
//Do something with grade
}
else
{
//Do something to warn of invalid input.
}
You should use:
int maths_grade = int.Parse(Console.ReadLine());
because ReadLine returns string, then you need to parse it to get int. But this will throw an exception if line won't contain valid string (number). You can better check this by using TryParse version:
string line = Console.ReadLine();
int maths_grade;
if (!int.TryParse(line, out maths_grade))
{
// Do some kind of error handling
}