# Practice questions on Loop and loop

## Level 1

1.
What would be the output of:
```#include <stdio.h>
int main(){
for(int i = 0;1;i++){
printf("%d\n",i);
}
return 0;
}
```

2.
What would be the output of:
```#include <stdio.h>
int main( )
{
int x = 10, y = 3, z;
for(z = 0; z<x; )
z = z++ +y;
printf("%d\n", z) ;
return 0;
}
```

3.
What would be the output of:
```#include <stdio.h>
int main(){
int x = 10, y = 20, z;
for(z = 0,z<y;z++){
if(z==x){
printf("%d\n",z);
}
else{
break;
}
}
}
```

4.
Write the same code using the while loop.
```#include <stdio.h>
int main(){
for(int i = 0;1;i++){
printf("%d\n",i);
}
return 0;
}
```

## Level 2

1.
Take 10 integers from keyboard using loop and print their average value on the screen.
```#include <stdio.h>
int main()
{
int sum = 0,i;
for(i = 0;i<10;i++){
int x;
printf("Enter a number.\n");
scanf("%d",&x);
sum = sum+x;
}
printf("Average is %f\n",sum/10.0);
return 0;
}
```

2.
Print ASCII values and their equivalent characters. ASCII value vary from 0 to 255.
```#include <stdio.h>
int main()
{
int i;
for(i=0;i<255;i++)
{
printf("%c\n",i);
}
}
```

3.
Print the following patterns using loop :
a.
*
**
***
****
b.
*
***
*****
***
*
c.
1010101
10101
101
1

4.
Print multiplication table of 24, 50 and 29 using loop.
```#include <stdio.h>
int main()
{
int i;
for(i=1;i<=10;i++)
{
printf("24 * %d\t=\t%d\n",i,24*i);
}
}
```

5.
Write an infinite loop.

6.
Factorial of any number n is represented by n! and is equal to 1*2*3*....*(n-1)*n. E.g.-
4! = 1*2*3*4 = 24
3! = 3*2*1 = 6
2! = 2*1 = 2
Also,
1! = 1
0! = 0
Write a C program to calculate factorial of a number.
```#include <stdio.h>
int main()
{
int x,fact=1,i;
printf("Enter a number\n");
scanf("%d",&x);
for(i = x; i>=1 ;i--){
fact = fact*i;
}
printf("Factorial is %d\n",fact);
}
```

7.
Write a C program to find greatest common divisor (GCD) or highest common factor (HCF) of given two numbers.
```#include <stdio.h>
int main()
{
int x,y,gcd,lcm,t,b,a;
printf("Enter two integers\n");
scanf("%d %d", &x, &y);
a=x;
b=y;
while (b != 0)
{
t = b;
b = a % b;
a = t;
}
gcd = a;
lcm = (x*y)/gcd;
printf("GCD is %d and LCM is %d\n",gcd,lcm);
}
```

## Level 3

1.

2.

### A three digit number is called Armstrong number if sum of cube of its digit is equal to number itself.E.g.- 153 is an Armstrong number because (13)+(53)+(33) = 153.Write all Armstrong numbers between 100 to 500.

```#include <stdio.h>
int main()
{
int i;
for(i=1;i<=500;i++)
{
int sum = 0;
int t = i;
while(t!=0)
{
sum = sum+((t%10)*(t%10)*(t%10));
t = t/10;
}
if(sum==i)
{
printf("%d\n",i);
}
}
return 0;
}
```

3.

4.

5.

### Write a C program to find prime factor of a number.If a factor of a number is prime number then it is its prime factor.

```#include <stdio.h>
int main()
{
int x,i,j;

printf("Enter the number\n");
scanf("%d",&x);

printf("Prime factors of %d are:\n",x);

for(i=2;i<=x;i++){
//checking for factor
if(x%i==0){
//checking if i is prime or not
int p = 0;
for(j=2;j<i;j++){
if(i%j==0){
//i is not prime
p++;
break;
}
}
if(p==0){
//if p is 0
//then i is prime
printf("%d\n",i);
}
}
}
return 0;
}
```