Using Variables Inside Strings

How do I put a variable’s value inside a string (interpolate it into the string)?

plot.savefig('hanning(%d).pdf' % num)

The % operator, when following a string, allows you to insert values into that string via format codes (the %d in this case). For more details, see the Python documentation:

printf-style String Formatting

How to interpolate variables in strings in JavaScript, without concatenation?

You can take advantage of Template Literals and use this syntax:

`String text ${expression}`

Template literals are enclosed by the back-tick (` `) (grave accent) instead of double or single quotes.

This feature has been introduced in ES2015 (ES6).

Example

var a = 5;
var b = 10;
console.log(`Fifteen is ${a + b}.`);
// "Fifteen is 15.

How neat is that?

Bonus:

It also allows for multi-line strings in javascript without escaping, which is great for templates:

return `
    <div class="${foo}">
         ...
    </div>
`;

Browser support:

As this syntax is not supported by older browsers (mostly Internet Explorer), you may want to use Babel/Webpack to transpile your code into ES5 to ensure it will run everywhere.

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Side note:

Starting from IE8+ you can use basic string formatting inside console.log:

console.log('%s is %d.', 'Fifteen', 15);
// Fifteen is 15.

Using variables inside strings

In C# 6 you can use string interpolation:

string name = "John";
string result = $"Hello {name}";

The syntax highlighting for this in Visual Studio makes it highly readable and all of the tokens are checked.

Interpolate or use a variable inside a string in javascript

Combine the variable into the string properly:

 text: 'o consumo aumentou em '+qtd3+' luvas = '+qtd4+' caixas.'

Putting a variable into a string (quote)

You should use a string formatter here, or concatenation. For concatenation you'll have to convert an int to a string. You can't concatenate ints and strings together.

This will raise the following error should you try:

TypeError: unsupported operand type(s) for +: 'int' and 'str'

Formatting:

quote = "You are %d years old" % age
quote = "You are {} years old".format(age)

Concatenation (one way)

quote = "You are " + str(age) + " years old" 

Edit: As noted by J.F. Sebastian in the comment(s) we can also do the following

In Python 3.6:

f"You are {age} years old"

Earlier versions of Python:

"You are {age} years old".format(**vars())

R variable inside a string

variable2 <- paste0("I am argument:",variable1,"text continue")

How do I put variables inside javascript strings?

Note, from 2015 onwards, just use backticks for templating

https://stackoverflow.com/a/37245773/294884

let a = `hello ${name}`    // NOTE!!!!!!!! ` not ' or "

Note that it is a backtick, not a quote.

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If you want to have something similar, you could create a function:

function parse(str) {
    var args = [].slice.call(arguments, 1),
        i = 0;

    return str.replace(/%s/g, () => args[i++]);
}

Usage:

s = parse('hello %s, how are you doing', my_name);

This is only a simple example and does not take into account different kinds of data types (like %i, etc) or escaping of %s. But I hope it gives you some idea. I'm pretty sure there are also libraries out there which provide a function like this.

Insert variable values in the middle of a string

You can use string.Format:

string template = "Hi We have these flights for you: {0}. Which one do you want";
string data = "A, B, C, D";
string message = string.Format(template, data);

You should load template from your resource file and data is your runtime values.

Be careful if you're translating to multiple languages, though: in some cases, you'll need different tokens (the {0}) in different languages.

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