The term flow of control refers to the order in which a program's statments are executed. Following are the control flow statements in C language, which can be used to control the flow of a program.

• if-else-if
• ternary
• switch
• while
• for
• break
• continue

The if statement has the same function as other languages. It has three basic forms:

• if (expression) { statement }
• if (expression) { statement } else { statement }
• if (expression) { statement } else if { statement } else { statement }

The ? (ternary condition) operator is a more efficient form for expressing simple if statements. It has the following form:

expression₁ ? expression₂: expression₃

It simply states:

if expression₁ then expression₂ else expression₃

The C switch is similar to Pascal's case statement and it allows multiple choice of a selection of items at one level of a conditional where it is a far neater way of writing multiple if statements:

  1 switch (expression) {
  2  case item1:
  3 		 statement1;
  4 		 break;
  5  case item2:
  6 		 statement2;
  7 		 break;
  8                  .
  9                  .
 10                  .
 11                  .
 12                  .
 13                  .
 14                  .
 15  case itemn:
 16 		 statementn;
 17 		 break;
 18  default:
 19 		 statement;
 20 		 break;
 21 }

In each case the value of item_i must be a constant, variables are not allowed.

The break is needed if you want to terminate the switch after execution of one choice. Otherwise the next case would get evaluated. Note: This is unlike most other languages.

We can also have null statements by just including a ; or let the switch statement fall through by omitting any statements (see e.g. below).

The default case is optional and catches any other cases.

The while statement is similar to those used in other languages although more can be done with the expression statement -- a standard feature of C.

while(expression)

statement

Because the while loop can accept expressions, not just conditions, the following are all legal

• while (x-)
• while (x=x+1)
• while (x+=5)

Using this type of expression, only when the result of x-, x=x+1, or x+=5, evaluates to 0 will the while condition fail and the loop be exited.

The C for statement has the following form:

for (expression₁; expression₂; expression₃)

statement;

or {block of statements}

expression₁ initialises; expression₂ is the terminate test; expression₃ is the modifier (which may be more than just simple increment);

We have already met break in the discussion of the switch statement. It is used to exit from a loop or a switch, control passing to the first statement beyond the loop or a switch.

With loops, break can be used to force an early exit from the loop, or to implement a loop with a test to exit in the middle of the loop body. A break within a loop should always be protected within an if statement which provides the test to control the exit condition.

This is similar to break but is encountered less frequently. It only works within loops where its effect is to force an immediate jump to the loop control statement.

• In a while loop, jump to the test statement.
• In a do while loop, jump to the test statement.
• In a for loop, jump to the test, and perform the iteration.

Like a break, continue should be protected by an if statement. You are unlikely to use it very often.

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