Control flow allow you to change order of execution. It is important feature of C where you can instruct compiler to evaluate line of code according to you.
C provides two types of flow control
- Branching
- looping
Branching is deciding what action to take and looping is deciding how many times to take a certain action. Next we will see both types of C flow control in this tutorial.
2.1 if statement
if statement is used when a unit of code to be executed by a condition true or false.
The syntax is:-
| if ( expression) { statement 1; } statement 2; } Here else part is optional. The expression inside if() is evaluated, if it is true (that is, if expression has non zero value) then statment 1 is executed . if it is false(that, expression is zero) an else part , statment 2 is executed. |
Lets see some examples then things will be more cleared. Suppose you want to write a C programm to check in exam a student is pass or not based on given marks,
| #include<stdio.h> int main() { int marks; printf(“Enter the marks\n”); if (marks >= 30) printf(” Student is pass\n”);
} } Case 1: Suppose you enter 50 means if condition is true, the output will be:- Case 2 : Suppose you enter 20 means if condition is false then program wont print anything, the output will be:- |
Now you want to check a student is pass or fail based on given marks. lets try this C program.
| #include<stdio.h> int main() { int marks; printf(“Enter the marks\n”); if (marks >= 30) printf(” Student is pass\n”); } printf(” Student is fail\n”); } Case 1: Suppose you enter 20 means if condition is false, then this program execute lines after if statement, the output will be:- Case 2 : Suppose you enter 50 means if condition is true, then compiler execute both printf() and the output will be:- |
We can clearly see in above C program. when a student secure more than 30 marks the output of program is unexpected. Our intension was to print either pass or fail. In this case we need to use if – else statement. Now we check example C program of chapter 2.2