Added info; Fixed formatting; (#36329)

Added note on Scope
Fixed formatting of example and added better way to rewrite example.
This commit is contained in:
KartikSoneji
2019-07-15 19:01:55 +05:30
committed by Randell Dawson
parent 629da5329d
commit 72be29068a

View File

@ -11,28 +11,76 @@ It does exactly what it is named as. It goes to the mentioned occurence of the n
goto - The keyword used to go to the particular label.
label - this can be named anything.
# syntax
`goto label; //This takes the program flow to the next appearance of label.`
goto is something that transcends all loops. To be clearer on this point, here is an example.
# Syntax
```C++
goto label_name;
//This takes the program flow to the next appearance of label_name.
```
#include <iostream>
using std::cout;
Labels are defined as a name, followed by a colon (**:**)
```C++
label_name:
```
# Scope
int main() {
for(;;)
{
if(1)
goto label;
`goto` can only jump to a label in the **same scope** (set of braces - {}).
### Example:
```C++
#include <iostream>
int main(){
goto x:
std::cout << "Hello World"; //no text is printed.
x:
return 0;
}
label:
cout << "lol"; //here, goto is used to get out of an otherwise infinite loop. That is one of the only places where goto is tolerated.
int someFunction(){
x: //the program does not jump to this label becaue it is in another scope.
return 0;
}
```
[Try the code here!](https://wandbox.org/permlink/tG0aInbyuKJQC4ER)
**However, care must be taken to use goto very carefully.**
`goto` is something that transcends all loops. To be clearer on this point, here is an example.
```C++
#include <iostream>
using std::cout;
int main(){
for(;;){
if(1) goto label;
}
label:
cout << "lol";
//here, goto is used to get out of an otherwise infinite loop. That is one of the only places where goto is tolerated.
return 0;
}
```
[Try the code here!](https://wandbox.org/permlink/2zm4f4WMR7ybvJlQ)
Even though the above code works, a **much** better option is to structure your code such that `goto` is not needed for the program flow. For this reason, many modern programming languages (like java, javascript, python, etc.) do support `goto`. Instead, control statements like `break` and `continue` are used.
The above example can be rewritten using `break` as:
```C++
#include <iostream>
using std::cout;
int main(){
for(;;){
if(1) break;
}
cout << "lol";
return 0;
}
```
[Try the code here!](https://wandbox.org/permlink/faRaw7paaRwWGkln)
**However, care must be taken to use goto very carefully**, especially in the early days of coding as it can lead to crazy issues, if not understood well enough. `goto` violates the standard flow of the program, and as C++ is an object oriented language, goto should **NEVER EVER, EVER** be used in a normal program, under **ANY CIRCUMSTANCES**. The same effect can usually be replicated by using functions or loops, with the resulting code being easier to read as well as maintain.
#### The consequences of using goto are illustrated in this XKCD comic (#292)
![](https://imgs.xkcd.com/comics/goto.png)