87 lines
1.9 KiB
Markdown
87 lines
1.9 KiB
Markdown
---
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title: Short-Circuit Evaluation
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---
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# Short-Circuit Evaluation
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The Short-Circuit evaluation consists in checking or executing the second argument only if the first argument is not enough to determine the value of the expression.
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You can do a short-circuit evaluation with `&&` and `||` operators.
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### Example with `&&` Operator
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```c
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canOpenFile(filename) && openFile(filename); // If you can open the file then open it.
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```
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The example above is equivalent to:
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```c
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if ( canOpenFile(filename) ) {
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openFile(filename);
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}
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```
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### Example with `||` Operator
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```c
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isServerOn || startServer(); // If the server is not on then start it.
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```
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The example above is equivalent to:
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```c
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if ( !isServerOn ) {
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startServer();
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}
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```
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### A Real-World Example with `||` Operator
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```c
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#include <stdio.h>
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#include <stdlib.h>
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char *getName();
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int main(int argc, char *argv[]) {
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// Get the first argument passed via terminal
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char *name = argv[1];
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// If the name is not passed via terminal, then print a message and then get the name
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name || printf("Please give me your name:") && (name = getName());
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printf("Hello %s\n", name);
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}
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char *getName() {
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// Allocate memory
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char *name = (char*)malloc(30);
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scanf("%s", name);
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return name;
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}
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```
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### Example with Nested `if` Statements
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```c
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int i, j;
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scanf ( "%d %d", &i, &j );
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if ( i > 10 && j > 10 ) {
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printf("Both numbers are greater than 10! \n");
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}
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```
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The above example is equivalent to:
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```c
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int i, j;
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scanf ( "%d %d", &i, &j );
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if ( i > 10 ) {
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if ( j > 10 ) {
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printf("Both numbers are greater than 10! \n");
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}
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}
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```
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Notice when `if ( i > 10 )` fails, the statement is false and the check `if ( j > 10 )` is never run. `if ( i > 10 && j > 10 )` behaves exactly the same way, because if `i > 10` is false then the entire statement is automatically false, and there is no need to run an additional check.
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