Difference between for and while loops in C?

Question

hey so i just started programming (C) and i wanna know the difference between while and for loops, so i did a program to sum natural numbers with a for loop and it worked:

int sum = 0;
int count;
int num = 11;

for (count = 1; count <= num; count++){
    sum += count;
}
printf("Sum of numbers is: %d\n", sum);

Sum came out as 66 and count comes out as 11, but when i tried it in a while loop it came out wrong:

int kount = 1;
int ssum = 0;
int number = 11;
while(kount <= number){
    ++kount;
    ssum += kount;
}
printf("Ssum is: %d \n", ssum);
printf("Kount is %d \n", kount);

Here ssum comes out as 77 and kount comes out as 12. Can anyone explain why to a beginner like me?

Hey! Check the value of `count` / `kount` when you add to the sum! — M Oehm, Oct 24 '18 at 13:32
`++kount; ssum += kount;` Change the order of these to get for-loop-like behavior. — Lundin, Oct 24 '18 at 13:37
the value of count goes to 11 while the value of kount in the while code comes out as 12 and i have no idea why? — ooatman, Oct 24 '18 at 13:37
Changing the order worked! Can you explain why that happens? — ooatman, Oct 24 '18 at 13:38
`for` loops perform third statement, `count++`, after loop has completed (i.e. at end). — Fiddling Bits, Oct 24 '18 at 13:40
An alternative would be to initialize `kount` to `0` and change you're while loop to `while(kount < number)`. — Fiddling Bits, Oct 24 '18 at 13:42
`for(a;b;c){d;}` is broadly equivalent to `a;while(b){d;c;}` -- note the relative order of `c` and `d` inside the while loop. — Tim Randall, Oct 24 '18 at 13:43

Atharva Jawalkar · Answer 1 · 2018-10-24T13:45:32.637

2

just add line ++Kount after ssum+=kount and your problem will get solved.

int ssum = 0;
int kount = 1;
int number = 11;
while (kount <= number) {
    ssum += kount;
    ++kount;

}
printf("Ssum is: %d \n", ssum);
printf("Kount is %d \n", kount);

edited Oct 24 '18 at 13:45

answered Oct 24 '18 at 13:41

Atharva Jawalkar

166
1
12

console.log() is not C. – danglingpointer Oct 24 '18 at 13:43
oops i executed this code in node.js so you can replace console.log with printf. – Atharva Jawalkar Oct 24 '18 at 13:44

score 1 · Answer 2 · answered Oct 24 '18 at 13:40

1

Inside the body of your while loop try doing

ssum += kount; before you do ++kount;

answered Oct 24 '18 at 13:40

JamesOstmann

41
4

danglingpointer · Accepted Answer · 2018-10-24T13:49:46.983

1

The basic difference between for and while loop is all three steps initalization, test and increment are written in single line.

For loop:

int a ;
for(a= 0; a<10; a++)
{
    //do some stuff
}

While loop:

int a = 0;     // 1. Initialization step
while (a < 10) // 2. Test step
{
    // Do something
    a++;      // 3.Increment step. a++ is the same as saying a=a+1, 
}

Another way of comparing two numbers in while loop:

a=2;
b=3;
while (a < b)
{
    a++;
    printf("%d\n",a);
}

You can do this in one-liner using for loop.

for (a=2,b=3; a < b; a++,printf("%d\n",a));

edited Oct 24 '18 at 13:49

answered Oct 24 '18 at 13:48

danglingpointer

4,708
3
24
42

edit the x ni the `for loop` – José Manuel Ramos Oct 24 '18 at 13:49

score 0 · Answer 4 · answered Oct 24 '18 at 13:52

For safety reasons, it is often recommended to use for-loops instead of while.

With for-loops you have an "automatic" maximum loop count. When using while this depends on your code in the while-loop.

This is specially important on microcontrollers where your programm will get stuck if you do not leave the loop implementation.

Difference between for and while loops in C?

4 Answers4