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C if Statement
if (test expression) { statement/s to be executed if test expression is true; }
The if statement checks whether the text expression inside parenthesis () is true or not. If the
test expression is true, statement/s inside the body of if^ statement is executed but if test is false,
statement/s inside body of if^ is ignored.
Flowchart of if statement
Example 1: C if statement
Write a C program to print the number entered by user only if the number entered is
negative.
#include int main(){ int num; printf("Enter a number to check.\n"); scanf("%d",&num); if(num<0) { /* checking whether number is less than 0 or not. */ printf("Number = %d\n",num); }
/*If test condition is true, statement above will be executed, otherwise it will not be executed */ printf("The if statement in C programming is easy."); return 0; }
Output 1
Enter a number to check.
Number = - The if statement in C programming is easy.
When user enters -2 then, the test expression (num<0) becomes true. Hence, Number = -2 is
displayed in the screen.
Output 2
Enter a number to check. 5 The if statement in C programming is easy.
When the user enters 5 then, the test expression (num<0) becomes false. So, the statement/s
inside body of if^ is skipped and only the statement below it is executed.
C if...else statement
The if...else statement is used if the programmer wants to execute some statement/s when the
test expression is true and execute some other statement/s if the test expression is false.
Syntax of if...else
if (test expression) { statements to be executed if test expression is true; } else { statements to be executed if test expression is false; }
Flowchart of if...else statement
Nested if...else statement (if...elseif....else Statement)
The nested if...else statement is used when program requires more than one test expression.
Syntax of nested if...else statement.
if (test expression1){ statement/s to be executed if test expression1 is true; } else if(test expression2) { statement/s to be executed if test expression1 is false and 2 is true; } else if (test expression 3) { statement/s to be executed if text expression1 and 2 are false and 3 is true; } . . . else { statements to be executed if all test expressions are false; }
How nested if...else works?
The nested if...else statement has more than one test expression. If the first test expression is
true, it executes the code inside the braces{ } just below it. But if the first test expression is false,
it checks the second test expression. If the second test expression is true, it executes the
statement/s inside the braces{ } just below it. This process continues. If all the test expression are
false, code/s inside else is executed and the control of program jumps below the nested
if...else
The ANSI standard specifies that 15 levels of nesting may be continued.
Example 3: C nested if else statement
Write a C program to relate two integers entered by user using = or > or < sign.
#include int main(){ int numb1, numb2; printf("Enter two integers to check\n"); scanf("%d %d",&numb1,&numb2); if(numb1==numb2) //checking whether two integers are equal. printf("Result: %d = %d",numb1,numb2); else if(numb1>numb2) //checking whether numb1 is greater than numb2. printf("Result: %d > %d",numb1,numb2); else printf("Result: %d > %d",numb2,numb1); return 0; }
Output 1
Enter two integers to check. 5 3
Result: 5 > 3
Output 2
Enter two integers to check.
Result: -4 = -
C Programming Loops
Loops cause program to execute the certain block of code repeatedly until test condition is false.
Loops are used in performing repetitive task in programming. Consider these scenarios:
- You want to execute some code/s 100 times.
- You want to execute some code/s certain number of times depending upon input from
user.
These types of task can be solved in programming using loops.
There are 3 types of loops in C programming:
1. for loop
2. while loop
3. do...while loop
for Loop Syntax
for(initialization statement; test expression; update statement) { code/s to be executed; }
How for loop works in C programming?
The initialization statement is executed only once at the beginning of the for loop. Then the test
expression is checked by the program. If the test expression is false, for loop is terminated. But if
test expression is true then the code/s inside body of for loop is executed and then update
expression is updated. This process repeats until test expression is false.
This flowchart describes the working of for loop in C programming.
Output
Enter the value of n. 19 Sum=
In this program, the user is asked to enter the value of n. Suppose you entered 19 then, count is
initialized to 1 at first. Then, the test expression in the for loop,i.e., (count<= n) becomes true.
So, the code in the body of for loop is executed which makes sum to 1. Then, the expression +
+count is executed and again the test expression is checked, which becomes true. Again, the
body of for loop is executed which makes sum to 3 and this process continues. When count is 20,
the test condition becomes false and the for loop is terminated.
Syntax of while loop
while (test expression) { statement/s to be executed. }
The while loop checks whether the test expression is true or not. If it is true, code/s inside the
body of while loop is executed,that is, code/s inside the braces { } are executed. Then again the
test expression is checked whether test expression is true or not. This process continues until the
test expression becomes false.
Example of while loop
Write a C program to find the factorial of a number, where the number is entered by user.
(Hints: factorial of n = 123...n
/C program to demonstrate the working of while loop/ #include int main(){ int number,factorial; printf("Enter a number.\n"); scanf("%d",&number); factorial=1; while (number>0){ /* while loop continues util test condition number>0 is true / factorial=factorialnumber;
--number; } printf("Factorial=%d",factorial); return 0; }
Output
Enter a number. 5 Factorial=
do...while loop
In C, do...while loop is very similar to while loop. Only difference between these two loops is
that, in while loops, test expression is checked at first but, in do...while loop code is executed at
first then the condition is checked. So, the code are executed at least once in do...while loops.
Syntax of do...while loops
do { some code/s; } while (test expression);
At first codes inside body of do is executed. Then, the test expression is checked. If it is true,
code/s inside body of do are executed again and the process continues until test expression
becomes false(zero).
Notice, there is semicolon in the end of while (); in do...while loop.
Example of do...while loop
Write a C program to add all the numbers entered by a user until user enters 0.
/C program to demonstrate the working of do...while statement/ #include int main(){ int sum=0,num; do /* Codes inside the body of do...while loops are at least executed once. */ {
Example of break statement
Write a C program to find average of maximum of n positive numbers entered by user. But, if the
input is negative, display the average(excluding the average of negative input) and end the
program.
/* C program to demonstrate the working of break statement by terminating a loop, if user inputs negative number*/
include
int main(){ float num,average,sum; int i,n; printf("Maximum no. of inputs\n"); scanf("%d",&n); for(i=1;i<=n;++i){ printf("Enter n%d: ",i); scanf("%f",&num); if(num<0.0) break; //for loop breaks if num<0. sum=sum+num; } average=sum/(i-1); printf("Average=%.2f",average); return 0; }
Output
Maximum no. of inputs
Enter n1: 1. Enter n2: 12. Enter n3: 7. Enter n4: - Average=7.
In this program, when the user inputs number less than zero, the loop is terminated using break
statement with executing the statement below it i.e., without executing sum=sum+num.
In C, break statements are also used in switch...case statement. You will study it in C
switch...case statement chapter.
continue Statement
It is sometimes desirable to skip some statements inside the loop. In such cases, continue
statements are used.
Syntax of continue Statement
continue;
Just like break, continue is also used with conditional if statement.
For better understanding of how continue statements works in C programming. Analyze the
figure below which bypasses some code/s inside loops using continue statement.
Decision making are needed when, the program encounters the situation to choose a particular statement
among many statements. If a programmer has to choose one block of statement among many alternatives,
nested if...else can be used but, this makes programming logic complex. This type of problem can be
handled in C programming using switch statement.
Syntax of switch...case
switch ( n ) { case constant1: code/s to be executed if n equals to constant1 ; break; case constant2 : code/s to be executed if n equals to constant2 ; break; . . . default: code/s to be executed if n doesn't match to any cases; }
The value of n is either an integer or a character in above syntax. If the value of n matches
constant in case, the relevant codes are executed and control moves out of the switch statement.
If the n doesn't matches any of the constant in case, then the default codes are executed and
control moves out of switch statement.
out of switch statement.
Example of switch...case statement
Write a program that asks user an arithmetic operator('+','-','*' or '/') and two operands and
perform the corresponding calculation on the operands.
include
int main() { char o; float num1,num2; printf("Select an operator either + or - or * or / \n"); scanf("%c",&o); printf("Enter two operands: "); scanf("%f%f",&num1,&num2); switch(o) { case '+': printf("%.1f + %.1f = %.1f",num1, num2, num1+num2); break; case '-': printf("%.1f - %.1f = %.1f",num1, num2, num1-num2); break; case '': printf("%.1f * %.1f = %.1f",num1, num2, num1num2); break; case '/': printf("%.1f / %.1f = %.1f",num1, num2, num1/num2); break; default: /* If operator is other than +, -, * or /, error message is shown */ printf("Error! operator is not correct"); break; } return 0; }
Output
Enter operator either + or - or * or /
Enter two operands: 2.
2.3 * 4.5 = 10.
The break statement at the end of each case cause switch statement to exit. If break statement
is not used, all statements below that case statement are also executed.
