Decision Making in C

The Conditional statement in C allows you to make a decision based upon the result of the conditions. Such statements are called as Decision Making statements or Conditional Statements.

The C statements are executed sequentially in the order of how we write. There will be only the change when you use the jump based statements or functional call statements for certain calculations. In some situation, there will be a need for execution of statements based on conditional statements.

In C programming language, any non zero values are assumed as TRUE and zero or null values are assumed as FALSE.

Flow Chart for Decision Making 

    

                                               

The following are the various Decision-Making statements in C:

•  if statement
• if-else statement
• Nested if statement
• else-if statement
• goto statement
• switch statement
• Conditional Operator

C if statement

The ‘if’ statement in C is used to control the C program flow based on the if condition. If the condition in the ‘if statement’ is true, then the block of code will be executed, otherwise, it will be skipped. 

Syntax

If (condition)

{
	…..
	Code block;
	…..
}

#include

main()
{
  int a = 15;

  if (a<20) {
    printf("a is less than 20");
  }
}

Output

a is less than 20

C if-else statement

If there is a either way to execute in the program if the ‘if block’ is not executed, then the else block of the code will be executed.

Syntax

if (condition)

{

…..

Code block;

…..

}

else 

{

…..

Code block;

…..

}

If the condition in ‘if block’ is not true, then the else block will be executed.

Flowchart

Example Program

#include

void main()
{
  int a, b;

  printf("Enter the value for a: ");
  scanf("%d", &a);

  printf("\nPlease the value for b: ");
  scanf("%d", &b);

  if (a > b) {
    printf("\n a is greater than b");
  } else {
    printf("\n b is greater than a");
  }
}

Enter the value for a: 5
Please the value for b: 10
 b is greater than a

From the above program, the two numbers are compared and printed which number is greater.

Nested if-else statements

#include

main()
{
int x=5,y=10;

    if(x==5)
    {
        if(y==10)
        {
            printf("value of x is 5, and value of y is 10.");
        }
    }
    else
    {
        printf("x and y values are not 5 and 10");
    }
}

Output:

value of x is 5, and value of y is 10.

C else-if statements

This is an another if statement and used when if statements having multiple decisions.

Syntax

if (condition 1)

{

…..

Code block;

…..

}

else if(condition 2)

{

…..

Code block;

…..

}

else {

…..

Code block;

…..

}

Example Program

#include

main()
{
  int a, b;

  printf("Enter the value for a: ");
  scanf("%d", &a);

  printf("\nEnter the value for b: ");
  scanf("%d", &b);

  if (a > b)
  {
    printf("\n a is greater than b");
  }
  else if (b > a)
  {
    printf("\n b is greater than a");
  }
  else
  {
    printf("\n Both are equal");
  }
}

Output

Enter the value for a: 5
Enter the value for b: 10
 b is greater than a

In the above example program, else-if statement checks for another if condition. We can use as many else-if conditions in the code.

C goto Statement

In C, we have special type of Statements which does not execute based on some decisions or conditions. The goto statement in C are not based on any conditions but still it controls the flow. The goto statement is used to branch unconditionally within a program from one point to another. The use of goto statements are not encouraged in C programming but still it is used in some situations where the use of goto statements will be more desirable.

#include 

void main() {

   const int maxInput = 10;
   int i;
   double number, average, sum = 0.0;

   for (i = 1; i <= maxInput; ++i) {
      printf("%d. Enter a number: ", i);
      scanf("%lf", &number);

      // go to jump if the negative number is given
      if (number < 0.0) {
         goto jump;
      }
      sum += number;
   }

jump:
   average = sum / (i - 1);
   printf("Sum = %.2f\n", sum);
   printf("Average = %.2f", average);
}

Output

1. Enter a number: 10
2. Enter a number: 12
3. Enter a number: 4
4. Enter a number: -3
Sum = 26.00
Average = 8.67

Note: The goto statement in C program should be used very carefully as it may jump to out of the scope. The goto statements are used only when it is needed and useful for your code.