if(expression){  
    //code to be executed  
    }  

Flowchart of if statement in C:

Let’s see an example of if statement. 

    #include<stdio.h>    
    int main(){    
    int number=0;    
    printf("Enter a number:");    
    scanf("%d",&number);    
    if(number%2==0){    
    printf("%d is even number",number);    
    }    
    return 0;  
    }    

After executing the code, our output looks like

Enter a number:4
4 is even number

Find the largest number of the three in C.

    #include <stdio.h>  
    int main()  
    {  
        int a, b, c;   
         printf("Enter three numbers?");  
        scanf("%d %d %d",&a,&b,&c);  
        if(a>b && a>c)  
        {  
            printf("%d is largest",a);  
        }  
        if(b>a  && b > c)  
        {  
            printf("%d is largest",b);  
        }  
        if(c>a && c>b)  
        {  
            printf("%d is largest",c);  
        }  
        if(a == b && a == c)   
        {  
            printf("All are equal");   
        }  
    }  

After executing the code, our output looks like

Enter three numbers?
12 23 34
34 is largest 

If-else Statement in C

To perform two operations for a single condition, we need to use if-else statement. Here one is for correctness of that condition, & other is for the incorrectness of the condition. If and else block cannot be executed simultaneously.

Syntax:

    if(expression){  
    //code to be executed if condition is true  
    }else{  
    //code to be executed if condition is false  
    }  

Flowchart of the if-else statement 

Following example check whether a number is even or odd using if-else statement

    #include<stdio.h>    
    int main(){    
    int number=0;    
    printf("enter a number:");    
    scanf("%d",&number);     
    if(number%2==0){    
    printf("%d is even number",number);    
    }    
    else{    
    printf("%d is odd number",number);    
    }     
    return 0;  
    }    

After executing the code, our output looks like

enter a number:4
4 is even number

enter a number:5
5 is odd number

Flowing Program check whether a person is eligible to vote or not

#include <stdio.h>  
int main()  
{  
    int age;   
    printf("Enter your age?");   
    scanf("%d",&age);  
    if(age>=18)  
    {  
        printf("You are eligible to vote...");   
    }  
    else   
    {  
        printf("Sorry ... you can't vote");   
    }  
} 

After executing the code, our output looks like

Enter your age?18
You are eligible to vote...
Enter your age?13
Sorry ... you can't vote

If else-if ladder Statement

It is an extension of if-else statement, which is used to perform multiple cases for different conditions.

Flowchart of else-if ladder

#include<stdio.h>    
int main(){    
int number=0;    
printf("enter a number:");    
scanf("%d",&number);     
if(number==10){    
printf("number is equals to 10");    
}    
else if(number==50){    
printf("number is equal to 50");    
}    
else if(number==100){    
printf("number is equal to 100");    
}    
else{    
printf("number is not equal to 10, 50 or 100");    
}    
return 0;  
}  

After executing the code, our output looks like

enter a number:4
number is not equal to 10, 50 or 100

enter a number:50
number is equal to 50

Following Program is calculating the grade of the student according to the specified marks

#include <stdio.h>  
int main()  
{  
    int marks;   
    printf("Enter your marks?");  
    scanf("%d",&marks);   
    if(marks > 85 && marks <= 100)  
    {  
        printf("Congrats ! you scored grade A ...");   
    }  
    else if (marks > 60 && marks <= 85)   
    {  
        printf("You scored grade B + ...");  
    }  
    else if (marks > 40 && marks <= 60)   
    {  
        printf("You scored grade B ...");  
    }  
    else if (marks > 30 && marks <= 40)   
    {  
        printf("You scored grade C ...");   
    }  
    else   
    {  
        printf("Sorry you are fail ...");   
    }  
} 

After executing the code, our output looks like

Enter your marks?10
Sorry you are fail ...
Enter your marks?40
You scored grade C ...
Enter your marks?90
Congrats ! you scored grade A ...