Control Flow

Statements and Blocks

  • An expression like i+2, i++, or printf(...) terminated by a ; becomes a statement in C.
  • Braces { and } are used to group statements inside a compound statement or a block.

If-Else

  • In if-else the else part is optional.
  • if checks the numeric value of an expression after evaluating it.

We might do -

if(x)		//non-zero value implicitly means true 

//instead of

if(x != 0)

Else-if

  • Multiple cases can be made using else-if.
  • Additional case/error catching case can be a last else but it is optional.

Switch

switch(expression)
{
	case const-expr: statements 
	case const-expr: statements 
	default: statements
}

  • Each case is labeled by integer-valued constants or constant expressions.

  • All cases must be different.

  • default case is optional.

  • IMPORTANT NOTE - Switch is fall through i.e. if we do not break the flow after a case, then it goes to the next case until it is stopped explicitly.

  • Several cases can be attached to a single action using this fall through property.

#include<stdio.h>

int main()
{
	char sec;

	scanf("%s", &sec);

	switch (sec)
	{
	case 'a':
	case 'A':

	case 'b':
	case 'B':	

	case 'c':
	case 'C':	printf("Your class has 10 students.");
		break;

	case 'd':
	case 'D':	

	case 'e':
	case 'E':	printf("Your class has 11 students.");
		break;

	default: printf("Section not found.");
		break;

	}

	return 0;
}

Loops - While and For

  • for and while loops are basically the same thing.
  • All three - Initialization, Condition, and Update in a for loop are expressions and either of them can be omitted, but the semicolons must remain.
  • Without the condition, for loop is infinite, even if we do not update.
  • Multiple expression separated by comma are allowed in for loop.

for (int i = 0, j = 1; i < counti, j < countj; i++, j++)
{
	/* code */
}

Do-while

  • The condition check is at last so the body is executed atleast once.
  • Braces around a single statement inside do block is optional but the while part can be mistaken for start of a while loop.

Break and Continue

  • break causes an exit from the innermost enclosing loop or switch.
  • continue causes the next iteration of the loop to begin.
  • A continue has no meaning in switch.
  • IMPORTANT NOTE - A continue inside a switch inside a loop will cause the loop to jump to next iteration.

Goto and Labels

  • goto can jump to a label anywhere inside the same function. A label follows same naming conventions as that of variables.