#include<stdio.h>
int main(){
  int num,count=0;

  printf("Enter a number: ");
  scanf("%d",&num);

  while(num){
      num=num/10;
      count++;
  }
  printf("Total digits is:  %d",count);
  return 0;
}
Sample output:
Enter a number: 23
Total digits is:  2

#include<stdio.h>
int main(){
  int num,count=0;

  printf("Enter a number: ");
  scanf("%d",&num);

  for(;num!=0;num=num/10)
      count++;

  printf("Total digits is:  %d",count);

  return 0;
}
Sample output:
Enter a number: 456
Total digits is:  3

#include<stdio.h>

int countDigits(num);
int main(){
  int num,count;

  printf("Enter a number: ");
  scanf("%d",&num);

  count = countDigits(num);

  printf("Total digits is:  %d",count);
  return 0;
}

int countDigits(int num){
    static int count=0;

     if(num!=0){
          count++;
         countDigits(num/10);
    }

    return count;
}
Sample output:
Enter a number: 1234567
Total digits is:  7

#include<stdio.h>
int main(){
  int n1,n2,x,y;
  printf("\nEnter two numbers:");
  scanf("%d %d",&n1,&n2);
  x=n1,y=n2;
  while(n1!=n2){
      if(n1>n2)
           n1=n1-n2;
      else
      n2=n2-n1;
  }
  printf("L.C.M=%d",x*y/n1);
  return 0;
}
Alternate Solution:
#include<stdio.h>

int lcm(int,int);

int main(){
    int a,b,l;

    printf("Enter any two positive integers ");
    scanf("%d%d",&a,&b);
 
    if(a>b)
         l = lcm(a,b);
    else
         l = lcm(b,a);
   
    printf("LCM of two integers is %d",l);

    return 0;
}

int lcm(int a,int b){
  
    int temp = a;

    while(1){
         if(temp % b == 0 && temp % a == 0)
             break;
         temp++;
    }

   return temp;
}

#include<stdio.h>

int lcm(int,int);

int main(){

   
    int a,b=1;
    printf("Enter positive integers. To quit press zero.");

    while(1){
         scanf("%d",&a);
         if(a<1)
             break;
         else if(a>b)
             b = lcm(a,b);
         else
             b = lcm(b,a);
    }

    printf("LCM is %d",b);

    return 0;
}

int lcm(int a,int b){
 
    int temp = a;

    while(1){
         if(temp % b == 0 && temp % a == 0)
             break;
         temp++;
    }

    return temp;
}