discussed different conditional statements (if, if-else, if-else if-else, switch-case) and sample practice codes.

1. Structured Programming Language
Conditional Statements in C
Mohammad Imam Hossain,
Lecturer, CSE, UIU
• if
• if-else
• if-else if-else
• Nested if
• switch

2. Introduction
• Till now, The instructions were executed in the
same order in which they appeared within the
program. (Sequence)
• Branching: one of several possible actions will be
carried out, depending on the outcome of the
logical test.
• Selection: One group of statements is selected
from several available groups.

3. Flow Chart of if Statement
if
condition
Body of if
True
False
Statement just below if

4. Syntax of if
if(condition)
{
statement/s that will execute if the
condition is true
}
statement/s just below if

5. Syntax of if
if(condition)
{
statement/s that will execute if the
condition is true
}
statement/s just below if

6. Syntax of if
if(condition)
{
statement/s that will execute if the
condition is true
}
statement/s just below if
True

7. Syntax of if
if(condition)
{
statement/s that will execute if the
condition is true
}
statement/s just below if
True

8. Syntax of if
if(condition)
{
statement/s that will execute if the
condition is true
}
statement/s just below if
True

9. Syntax of if
if(condition)
{
statement/s that will execute if the
condition is true
}
statement/s just below if

10. Syntax of if
if(condition)
{
statement/s that will execute if the
condition is true
}
statement/s just below if

11. Syntax of if
if(condition)
{
statement/s that will execute if the
condition is true
}
statement/s just below if
False

12. Syntax of if
if(condition)
{
statement/s that will execute if the
condition is true
}
statement/s just below if
False

13. Problem
• A program that will display a
number if the user enters
negative number otherwise
won’t display the number.

14. Solution
#include <stdio.h>
int main()
{
return 0;
}

15. Solution
#include <stdio.h>
int main()
{
int num;
printf("Enter the number: ");
scanf("%d",&num);
return 0;
}

16. Solution
#include <stdio.h>
int main()
{
int num;
printf("Enter the number: ");
scanf("%d",&num);
if(num<0){
}
return 0;
}

17. Solution
#include <stdio.h>
int main()
{
int num;
printf("Enter the number: ");
scanf("%d",&num);
if(num<0){
printf("You entered %dn",num);
}
return 0;
}

18. Solution
#include <stdio.h>
int main()
{
int num;
printf("Enter the number: ");
scanf("%d",&num);
if(num<0){
printf("You entered %dn",num);
}
printf("Exitn");
return 0;
}

20. Flow Chart of
if else
Statement
if
condition
Body of if
True
False
Statement just below if else
Body of else

21. Syntax of if else
if(condition)
{
statement/s that will execute if the condition is true
}
else
{
statement/s that will execute if the condition is false
}
statement/s just below if else

22. Syntax of if else
if(condition)
{
statement/s that will execute if the condition is true
}
else
{
statement/s that will execute if the condition is false
}
statement/s just below if else
true

23. Syntax of if else
if(condition)
{
statement/s that will execute if the condition is true
}
else
{
statement/s that will execute if the condition is false
}
statement/s just below if else
true

24. Syntax of if else
if(condition)
{
statement/s that will execute if the condition is true
}
else
{
statement/s that will execute if the condition is false
}
statement/s just below if else
true

25. Syntax of if else
if(condition)
{
statement/s that will execute if the condition is true
}
else
{
statement/s that will execute if the condition is false
}
statement/s just below if else
truefalse

26. Syntax of if else
if(condition)
{
statement/s that will execute if the condition is true
}
else
{
statement/s that will execute if the condition is false
}
statement/s just below if else
truefalse

27. Syntax of if else
if(condition)
{
statement/s that will execute if the condition is true
}
else
{
statement/s that will execute if the condition is false
}
statement/s just below if else
truefalse

28. Problem
• A program to check
whether an integer is even
or odd.

29. Solution#include <stdio.h>
int main()
{
return 0;
}

30. Solution#include <stdio.h>
int main()
{
int num;
printf("Enter the number: ");
scanf("%d",&num);
return 0;
}

31. Solution#include <stdio.h>
int main()
{
int num;
printf("Enter the number: ");
scanf("%d",&num);
if(num%2==0){
}
else{
}
return 0;
}

32. Solution#include <stdio.h>
int main()
{
int num;
printf("Enter the number: ");
scanf("%d",&num);
if(num%2==0){
printf("Evenn");
}
else{
}
return 0;
}

33. Solution#include <stdio.h>
int main()
{
int num;
printf("Enter the number: ");
scanf("%d",&num);
if(num%2==0){
printf("Evenn");
}
else{
printf("Oddn");
}
return 0;
}

34. Solution#include <stdio.h>
int main()
{
int num;
printf("Enter the number: ");
scanf("%d",&num);
if(num%2==0){
printf("Evenn");
}
else{
printf("Oddn");
}
printf("Exitn");
return 0;
}

35. Flow Chart of
if-else if-else
Statement

36. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else

37. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
true

38. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
true

39. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
true

40. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
truefalse
true

41. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
truefalse
true

42. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
truefalse
true

43. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
truefalse
truefalse
true

44. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
truefalse
truefalse
true

45. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
truefalse
truefalse
true

46. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
truefalse
truefalse
truefalse

47. Syntax of if – else if -else
if (condtion1)
{
statement/s that will execute if condition 1 is true.
}
else if (condition2)
{
statement/s that will execute if the condition 2 is true.
}
...
...
else if (condition n)
{
statement/s that will execute if the condition n is true.
}
else
{
statement/s that will execute if all conditions are false.
}
statement/s below if-else if-else
truefalse
truefalse
truefalse

48. Problem
• A program to compare two integers and show the
corresponding result (<,=,>).

49. Solution
#include <stdio.h>
int main()
{
return 0;
}

50. Solution
#include <stdio.h>
int main()
{
int num1,num2;
printf("Enter two integers: ");
scanf("%d %d",&num1,&num2);
return 0;
}

51. Solution
#include <stdio.h>
int main()
{
int num1,num2;
printf("Enter two integers: ");
scanf("%d %d",&num1,&num2);
if(num1>num2){
printf("first number is biggern");
}
return 0;
}

52. Solution
#include <stdio.h>
int main()
{
int num1,num2;
printf("Enter two integers: ");
scanf("%d %d",&num1,&num2);
if(num1>num2){
printf("first number is biggern");
}
else if(num1==num2){
printf("Both numbers are equaln");
}
return 0;
}

53. Solution
#include <stdio.h>
int main()
{
int num1,num2;
printf("Enter two integers: ");
scanf("%d %d",&num1,&num2);
if(num1>num2){
printf("first number is biggern");
}
else if(num1==num2){
printf("Both numbers are equaln");
}
else{
printf("num2 is biggern");
}
return 0;
}

54. Syntax of Nested if
if(condition)
{
if(condition)
{
statement;
}
else
{
statement;
}
}
else
{
statement;
}
Nested if else statement is
same like if else
statement, where new
block of if else statement
is defined in existing if or
else block statement.

55. Problem
• A program to check for a valid username and
password. If the username and password is correct
then show “Login Successful” message in the output.

56. Solution#include <stdio.h>
int main()
{
return 0;
}

57. Solution#include <stdio.h>
int main()
{
char uname;
int pass;
printf("Enter the user-name and password: ");
scanf(" %c %d",&uname,&pass);
return 0;
}

58. Solution#include <stdio.h>
int main()
{
char uname;
int pass;
printf("Enter the user-name and password: ");
scanf(" %c %d",&uname,&pass);
if(uname=='i'){
}
else{
}
return 0;
}

59. Solution#include <stdio.h>
int main()
{
char uname;
int pass;
printf("Enter the user-name and password: ");
scanf(" %c %d",&uname,&pass);
if(uname=='i'){
if(pass==1234){
printf("Login successfuln");
}
else{
printf("Incorrect passwordn");
}
}
else{
}
return 0;
}

60. Solution#include <stdio.h>
int main()
{
char uname;
int pass;
printf("Enter the user-name and password: ");
scanf(" %c %d",&uname,&pass);
if(uname=='i'){
if(pass==1234){
printf("Login successfuln");
}
else{
printf("Incorrect passwordn");
}
}
else{
printf("Incorrect user-name, try again.");
}
return 0;
}

61. Flow Chart of switch

62. Syntax of switch
switch(expression)
{
case constant-expression :
statement(s);
break; ///optional
case constant-expression :
statement(s);
break; ///optional
… …
/// you can have any number of case statements.
default : ///Optional
statement(s);
}
When the variable being
switched on is equal to a case,
the statements following that
case will execute until a break
statement is reached.

63. Syntax of switch
switch(expression)
{
case constant-expression :
statement(s);
break; ///optional
case constant-expression :
statement(s);
break; ///optional
… …
/// you can have any number of case statements.
default : ///Optional
statement(s);
}
When a break statement is
reached, the switch terminates,
and the flow of control jumps to
the next line following the
switch statement.

64. Syntax of switch
switch(expression)
{
case constant-expression :
statement(s);
break; ///optional
case constant-expression :
statement(s);
break; ///optional
… …
/// you can have any number of case statements.
default : ///Optional
statement(s);
}
Not every case needs to contain
a break. If no break appears, the
flow of control will fall
through to subsequent cases
until a break is reached.

65. Problem
• A program that takes input a grade(char) from user
and categorize it as “Excellent”, ”Well done”, ” You
passed”, “Better try again”, “Invalid grade”.

66. Solution
#include <stdio.h>
int main()
{
char ch;
scanf(" %c",&ch);
switch(ch){
case 'A':
printf("Excellentn");
break;
case 'B':
case 'C':
printf("Well donen");
break;
case 'D':
printf("You passedn");
break;
case 'F':
printf("Try againn");
break;
default:
printf("Invalid graden");
}
printf("Exitn");
return 0;
}

67. References
• https://www.programiz.com/c-programming
• https://www.tutorialspoint.com/cprogramming
• http://www.codeforwin.in/2015/05/basic-
programming-practice-problems.html
• Programming with C, Schaum’s Outlines 3rd Edition,
chapter 6  6.1,6.2,6.7