Decision Control Instruction In C: IF

So far we’ve seen that the code in C program gets executed in sequential order i.e., as and when the code appears in the source code. But today lets see how we can change the sequence of or order of execution using decision control instruction like if statement.

General form of if statement

if( some_condition )
statement;

By default, if statement executes only the next instruction present under it. But if you want to execute some block of code, then you must enclose it inside curly braces as shown below.

if( some_condition )
{
statement_1;
statement_2;
some_logic;
function_calls;
etc;
}

in above code, some_condition can be anything from a simple true(non-zero number) or false(0) or any expression returning 0 or any non-zero number.

Statements inside if statements curly braces can be anything from multi-line statements, function calls, some arithmetic operations etc.

 
#include < stdio.h >

int main()
{
    int a;
    printf("IBM\n");
    printf("Enter value for a \n");
    scanf("%d", &a);

    if(a > 10)
    {
        printf("Microsoft\n");
        printf("Oracle\n");
    }

    printf("Amazon\n");
    printf("Apple\n");    

    return 0;
}

Output:
IBM
Enter value for a
5
Amazon
Apple

Here user entered value for variable a is less than 10. So the code inside if block doesn’t get executed. So printing of Microsoft and Oracle gets skipped.

 
#include < stdio.h >

int main()
{
    int a;
    printf("IBM\n");
    printf("Enter value for a \n");
    scanf("%d", &a);

    if(a > 10)
    {
        printf("Microsoft\n");
        printf("Oracle\n");
    }

    printf("Amazon\n");
    printf("Apple\n");    

    return 0;
}

Output:
IBM
Enter value for a
14
Microsoft
Oracle
Amazon
Apple

For the same program, user entered value for variable a as 14, which is greater than 10. So all the company names gets printed on the console window as shown in above output section.

We can even remove condition statement inside if statement

 
#include < stdio.h >

int main()
{
    int a;
    printf("IBM\n");
    printf("Enter value for a \n");
    scanf("%d", &a);

    if(a)
    {
        printf("Microsoft\n");
        printf("Oracle\n");
    }

    printf("Amazon\n");
    printf("Apple\n");    

    return 0;
}

Output 1:
IBM
Enter value for a
1
Microsoft
Oracle
Amazon
Apple

Output 2:
IBM
Enter value for a
0
Amazon
Apple

Output 3:
IBM
Enter value for a
-5
Microsoft
Oracle
Amazon
Apple

In above example, when user enters 0 the condition becomes false, so the block of code inside if statement doesn’t get executed. When the user enters any number other than 0, its considered as true, so the code inside if statement gets executed.

Scanf(): For user input

In above c program we are asking user to enter the values for variable a and b. You can know more about scanf() method/function in this video tutorial: Using Scanf in C Program

Decision Control Instruction In C: IF

For full C programming language free video tutorial list visit:C Programming: Beginner To Advance To Expert