## 5.2 Control structures

> 5.2.1 apply |  |
> 5.2.2 break |  |
> 5.2.3 breakpoint |  |
> 5.2.4 continue |  |
> 5.2.5 else |  |
> 5.2.6 export |  |
> 5.2.7 exportto |  |
> 5.2.8 for |  |
> 5.2.9 if |  |
> 5.2.10 importfrom |  |
> 5.2.11 keepring |  |
> 5.2.12 load |  |
> 5.2.13 quit |  |
> 5.2.14 return |  |
> 5.2.15 while |  |
> 5.2.16 ~ (break point) |  |

A sequence of commands surrounded by curly brackets (`{` and `}`) is a so-called block. Blocks are used in SINGULAR in order to define procedures and to collect commands belonging to `if`, `else`, `for` and `while` statements and to the `example` part in libraries. Even if the sequence of statements consists of only a single command it has to be surrounded by curly brackets! Variables which are defined inside a block are not local to that block. Note that there need not be an ending semicolon at the end of the block.

`Example:`

      if ( i>j )
      {
        // This is the block
        int temp;
        temp=i;
        i=j;
        j=temp;
        kill temp;
      }

User manual for Singular version 4-0-3, 2016, generated by texi2html.