Control Flow

Conditionals

soup has a couple of constructs allowing the user to execute certain instructions based on the value of a boolean expression.

if

if [expression] {
    ...
}

The if construct allows for the execution of a collection of instructions only if a boolean expression evaluates to true.

Example 1:

printf("Before if\n");

if true {
    printf("Inside if\n");
}

printf("After if\n");

Output:

Before if
Inside if
After if

Example 2:

printf("Before if\n");

if 1 == 2 {
    printf("Inside if\n");
}

printf("After if\n");

Output:

Before if
After if

if-else

if [expression] {
    ...
} else {
    ...
}

The if-else construct allows for the execution of a collection of instructions only if a boolean expression evaluates to true, and a separate collection of instructions only if it evaluates to false.

Example 1:

printf("Before if-else\n");

if 99 < 100 {
    printf("Inside if\n");
} else {
    printf("Inside else\n");
}

printf("After if-else\n");

Output:

Before if-else
Inside if
After if-else

Example 2:

printf("Before if-else\n");

if (2 <= 3) && (5 == 6) {
    printf("Inside if\n");
} else {
    printf("Inside else\n");
}

printf("After if-else\n");

Output:

Before if-else
Inside else
After if-else

Loops

while

while [expression] {
    ...
}

The while loop allows for the execution of a collection of instructions repeatedly as long as a boolean expression evaluates to true.

Example:

int x = 1;
while x <= 5 {
    printf("x = {}\n", x);
    x += 1;
}

Output:

x = 1
x = 2
x = 3
x = 4
x = 5

An oft-forgotten aspect of writing while loops is the crucial updating of the condition that keeps the while loop looping. Consider the same example, but with the easily forgettable x += 1 line omitted:

int x = 1;
while x <= 5 {
    printf("x = {}\n", x);
}

Output:

x = 1
x = 1
x = 1
x = 1
x = 1
x = 1
x = 1
...

Since we are no longer updating the value of x, it will always be 1, the expression x <= 5 will never become false, and therefore the loop never exits.