Flow of Control

Flow of Control
Statements

In C, a statement is terminated by a semicolon.
An expression becomes a statement when it is terminated by a semicolon.
Braces, can be used to group a set of statements together into a block.

If-Else

C provides an if-else statement for use in making decisions. The syntax is:

if (expression)

statement or block #1

else

statement or block #2

The else is optional.

If the expression is true, a non-zero value, statement or block #1 is executed. If it is false, or zero, statement or block #2 is executed.

If-Else statements can be linked together providing a multi-way decision. The syntax is:

if (expression)

statement or block #1

else if (expression)

statement or block #2

else

statement or block #3

Switch

A switch statement is a multi-way decision statement, which tests whether an expression matches one of a selection of constants and branches accordingly. The following snipet of code, which increments the int vowel each time a vowel is found, and the int other, each time any other character is found, shows an example.

switch (c) {

case ‘a’:

case ‘e’:

case ‘i’:

case ‘o’:

case ‘u’:

vowel++;

break;

default:

other++;

}

The break statement breaks out of a loop or switch statement.

Loops

C defiines three different loops: for loops. while loops and do-while loops.

The syntax of a while loop is:

while (expression)

statement or block

The syntax of a for loop is:

for (expression #1; expression #2; expression #3)

statement or block

The above statement is equivalent to:

expression #1;

while (expression #2) {

statement or block

expression #3;

}

The following function calculates n! … n * (n-1) * … * 3 * 2 * 1
Parameters and return values will be presented later. For now, lets just say the function, factorial accepts as input an integer representing the number we want to calculate a factoral for and returns a long, the factorial.

long factorial(int n)

{

int i;

long fact = 1;;

for (i=n; i> 0; i--)

fact = fact * i;

return fact;

}

The syntax of a do-while loop is:

statement or block

while (expression);