# Debugging Operations

In circom there is an operation that can be used while developing circuits to help the programmer debug (note that there are no input/output operations on the standard input/output channels). To this end, the operation `log`

has as parameter a non-conditional expression (i.e., not including the `?`

`;_`

operator). The execution of this instruction prints the result of the evaluation of the expression in the standard error stream. As examples consider:

```
log(135);
log(c.b);
log(x==y);
```

Since circom 2.0.6, operation `log`

admits a list of non-conditional expressions and also strings written in the standard way. For instance:

```
log("The expected result is ",135," but the value of a is",a);
```

Finally, this operations admits an empty list of expressions which is equivalent to print an end-of-line. The next two instructions are equivalent:

```
log("");
log();
```