C - If, If-else and Nested If-else Statements

For Decision making, C uses the keyword if. The general form of the if statement is if(text_expression) statement1; The test expression should always be enclosed in parentheses. If the test_expression is nonzero(true) then the statement statement1 is executed;

If Statement

For Decision making, C uses the keyword if. The general form of the if statement is
if(text_expression)
statement1;
The test expression should always be enclosed in parentheses. If the test_expression is nonzero(true) then the statement statement1 is executed; Otherwise statement1 is skipped and control passes to the next statement. The statement1 can be a single statement or compound statement. The statement1 part of the if statement is the body of the if statement. This construct is shown in following flowchart. 
If Statement
If Statement

C Code

#include<stdio.h>
int main(void){
     int marks;
        printf("Enter Marks :");
        scanf("%d",&marks);
             if(marks>=40)
                 printf("Passed");
      return 0;
}

C Output

Enter Marks: 50
Passed

If -Else Statement

The if - else statement is also used for decision making purpose, C uses the keyword if-else. The general form of the if-else statement is,
if(test_expression)
 statement1;
else 
 statement2;
The if statement executes a single statement or a compound statement, when the test expression is true or nonzero. It does nothing when the test expression is not true.
C - If - else Statement
IF-ELSE STATEMENT
When the test expression is true or nonzero, then the body of if is executed and control passes to the next statement immediately following the if-else construct. But if the expression is not true or zero then the body of else is executed.

C Code

#include<stdio.h>
int main(void)
{
 int g;
 printf("Enter Your Marks\n");
 scanf("%d",&g);
 if (g>=60)
  printf("you passed\n");
 else
  printf("you failed\n");
}

C - Output

Condition1;
Enter Your Marks
45
you failed
Condition 2;
Enter Your Marks
61
you passed 

Nested If-Else Statement

The meaning of nesting is to have same construct within itself. Nesting means statement inside statement. Previously we learn about if-else statement, we identified a set of statements as the if block ans another set as the else block. The statement within the if-else statements could be another if or if-else statement. So this type of statement is called a nested conditional statement. This inner conditional expression is said to be nested within the outer one.

C Code

if(expression 1)
 if(expresssion2)
  statement1;
 else
  statement2;
else
  if(expresssion2)
  statement3;
 else
  statement4;
The statements can be surrounded by compound statement, if there exist more than one statement or other statement.

C Code

#include<stdio>
int main(void){
 int n,v;
 printf("Enter 2 Numbers:");
 scanf("%d%d",&n,&v);
 if(n>v)
  printf("first is larger");
 else
  if(n<v)
   printf("second is larger\n");
  else
   printf("both numbers are equal\n");
  return 0;
}

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