Control Flow

• Decisions - if then else
• More decisions - switch
• Loops - while, do while, for
• Keyword-break
• Keyword-continue

Decisions - if then

• Parentheses surround the test
• One statement becomes the “then part”
• If more are required, braces must be used

scanf("%i", &i);
 
if(i > 0)
{
  printf("a positive number was entered\n");
}
 
if(i < 0)
{
  printf("a negative number was entered\n");
  i = -i;
}

if then else

• An optional else may be added
• One statement by default, if more are required, braces must be used

if(i>0)
{
  printf("i is positive\n");
}
else
{
  printf("i is negative\n");
}

Nesting if-s

• else associates with the nearest if

Example :

int i = 100;
if(i>0)
{
  if(i>1000)
  {
  	printf("i is big\n");
  }
  else
  {
  	printf("i is reasonable\n");
  }
}

Result : i is reasonable

Example :

int = -20;
if(i>0)
{
  if(i>1000)
  {
    printf("i is big\n");
  }
}
else
{
  printf("i is negative\n");
}

Result : i is negative

switch

C supports a switch for multi-way decision making

switch(c) 
{ 
  case ‘a’:  case ‘A’: 
  printf("area = %.2f\n", r * r * pi); 
  break;
    
  case ‘c’: case ‘C’: 
  printf("circuinference — %.2f\n", 2 * r * pi); 
  break; 
    
  case ‘q’: 
  printf("quit option chosen\n”); 
  break; 
    
  default: 
  printf ("unknown option chosen\n”); 
  break; 
}

while Loop

• The simplest C loop is the while
• Parentheses must surround the condition
• One statement forms the body of the loop
•  Braces must be added if more statements are to be executed

Example:

int j = 5;
while(j>0)
{
  printf("j = %i\n", j--);
}

j = 5
j = 4
j = 3
j = 2
j = 1

int j = 5;
printf("start\n");
do
{
  printf("j = %i\n", j--);
}
while(j>0);
printf("stop\n");

start
j = 5
j = 4
j = 3
j = 2
j = 1
stop

int j = -10;
printf("start\n");
do
{
  printf("j = %i\n", j);
  j--;
}
while(j>0);
printf("stop\n");

start
j = -10
stop

for Loop

for encapsulates the essential elements of a loop into one statement

for(initial-part; while-condition; update-part)
{
 body; 
}

 Example :

int j;
for(j = 5; j > 0; j--)
{
printf("j = %i\n",j);
}

Result :

j = 5
j = 4
j = 3
j = 2
j = 1

Example :

for(j = 5; j > 0; j--)
{
  printf("j  = %i",j);
  printf("%s\n", ((j%2==0)?"even","odd"));
}

Result :

j = 5 odd
j = 4 even
j = 3 odd
j = 2 even
j = 1 odd

Stepping With for

Unlike some languages, the for loop is not restricted to stepping up or down by 1

#include <math.h> 
int main(void) 
{ 
double angle; 
for(angle = 0.0; angle < 3.14159; angle  +=  0.2)
 {
printf("sine of %.1lf is %.2lf\n”, angle, sin(angle)); 
return 0; 
 }
}

int i, j, k; 
for(i = 0, j = 5, k = -1; i < 10; i++, j++, k--)

• if you dont want to use initial part and update part than you can use as shown below Example :
  
  1

  for(; i<10;)

• and if you dont want to use initial part,condition and update part than it creates an infinite loop so you can use as shown below Example :
  
  1

  for(;;)