Let?s start with an example to remember previous course.

Write a program that enters a final grade of student and prints if the student passed or failed. (40 and above passed)

#include<stdio.h>

int main(){

int grade;

printf(?Enter the grade: ?);

scanf(?%d?,&grade);

if(grade>=40)

printf(?Passed.?);

if(grade<40)

printf(?Failed.?);

return 0;

}

If we write

if(1)

printf(?Hello!?);

It will accept this as true. Any number which is nonzero will be accepted true. Just

if(0)

printf(?Hello?);   //won?t print anyhing on the screen.

*An Extreme Example

Compare both of the below.

1-What is the output of this?

int x=8; y=5;

if(x==y)

printf(?%d is equal to %d.?,&x,&y);

This will print nothing.

2-What is the output of this?

int x=8; y=5;

if(x=y)

printf(?%d is equal to %d.?,&x,&y);

This condition is ?x=y?. This is not comparing them. Just assigning y to x. It makes x?s value 5.

if(x=y) means if(5). And 5 is nonzero, so this is true. And it will print ?5 equals 5? on the screen.

What if we make the values like that?

int x=8, y=0;

if(x=y)

printf(?%d is equal to %d.?,&x,&y);

It will make x?s value 0. İf(0) means it is false. Therefore, it will print nothing.

Ex:Write a program that allows the user to enter an integer. This program will print whether the integer is even or odd.

#include<stdio.h>

int main(){

int x;

printf(?Enter an integer: ?);

scanf(?%d?,&x);

if(x%2==0)

printf(?It?s even.?)

if(x%2==1)

printf(?It?s odd.?);

return 0;

}

Let?s make a different example:

Find the output of them. Assume that i=1, j=2, k=3.

printf(?%d?, i==1);       // 1

printf(?%d?, k<j);         //0

printf(?%d?, k!=4);       //1

printf(?%d?, i%2==1);  // 1

The results of them must be 1 or 0. Because all of them is condition, they can be true or false, not anything else.

If/else statement

if ( condition )

statement1;

else

statement2;

If if is true, else is ignored. Let?s cover this part with an example.

Ex: Write a program that allows the user to enter the final grade of a student.

If the student?s grade is larger than or equal to 50, then;

1-assign a character variable the letter ?A?,

2-print the letter and the word ?Passed?.

If not, then;

1-assign the character variable the letter ?F?,

2-print the letter and the word ?Failed?.

#include<stdio.h>

int main(){

int grade;

char letter;

printf(?Enter the grade: ?);

scanf(?%d?,&grade);

if(grade>=50){

letter=?A?;

printf(?You passed with the letter %c.?, letter);

}

else{

letter=?F?;

printf(?You failed with the letter %c.?, letter);

}

return 0;

}

If grade is 90, it won?t execute else.

If grade is 10, it will execute if, then it will execute also else part.

Nested if/else statements

Ex:Write a program that allows the user to enter an integer. Find and print if the integer is positive or negative or equal.

#include<stdio.h>

int main(){

int num;

printf(?Enter a number: ?);

scanf(?%d?,&num);

if(num==0)

printf(?Number is equal to zero.?);

else{

if(num<0)

printf(?Number is negative?);

else

printf(?Number is positive?);

}

return 0;

}

For this example, no need to add brackets for first else. So we use this type of statements like that:

if(num==0)

printf(??…?);

else if(num<0)

printf(???.?);

else if(num<5)

printf(???.?);

else if(num<19)

printf(???.?);

else    //this else part is for the other conditions except conditions above.

printf(????);

»Extra:

Answer is in the following lesson;)

?Answer of previous lesson’s extra:

We have talked about this. If condition is nonzero, then it is accepted as true. So it will print

“Yes, this is true”

on the screen.

See you soon ! 🙂