Question:How to convert string to int without using library functions in c programming language 

#include<stdio.h>

int stringToInt(char[] );
int main(){
  
    char str[10];
    int intValue;

    printf("Enter any integer as a string: ");
    scanf("%s",str);

   intValue = stringToInt(str);

    printf("Equivalent integer value: %d",intValue);

    return 0;
}

int stringToInt(char str[]){
    int i=0,sum=0;

    while(str[i]!='\0'){
         if(str[i]< 48 || str[i] > 57){
             printf("Unable to convert it into integer.\n");
             return 0;
         }
         else{
             sum = sum*10 + (str[i] - 48);
             i++;
         }
    }
    return sum;
}
Sample output:
Enter any integer as a string: 123
Equivalent integer value: 123

Question:Program in c to print 1 to 100 without using loop 

#include<stdio.h>

int main(){
    int num = 1;

    print(num);

    return 0;
}
int print(num){
    if(num<=100){
         printf("%d ",num);
         print(num+1);
    }
}
Sample output:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100

Question:Code for swapping in c 

#include<stdio.h>
int main(){
    int a,b,temp;
   
    printf("Enter any two integers: ");
    scanf("%d%d",&a,&b);
    printf("Before swapping: a = %d, b=%d",a,b);

    temp = a;
    a = b;
    b = temp;
    printf("\nAfter swapping: a = %d, b=%d",a,b);

    return 0;
}

Question:C program for swapping of two numbers using pointers 

#include<stdio.h>

int main(){

    int a,b;
    int *ptra,*ptrb;
    int *temp;

    printf("Enter any two integers: ");
    scanf("%d%d",&a,&b);

    printf("Before swapping: a = %d, b=%d",a,b);

    ptra = &a;
    ptrb = &b;

     temp = ptra;
    *ptra = *ptrb;
    *ptrb = *temp;

    printf("\nAfter swapping: a = %d, b=%d",a,b);
    return 0;
}
Sample output:
Enter any two integers: 5 10
Before swapping: a = 5, b=10
After swapping: a = 10, b=10

Question:Swapping program in c using function 

#include<stdio.h>

void swap(int *,int *);
int main(){

    int a,b;
   
    printf("Enter any two integers: ");
    scanf("%d%d",&a,&b);

    printf("Before swapping: a = %d, b=%d",a,b);

    swap(&a,&b);

    printf("\nAfter swapping: a = %d, b=%d",a,b);
    return 0;
}

void swap(int *a,int *b){
    int *temp;
    temp = a;
    *a=*b;
    *b=*temp;
}
Sample output:
Enter any two integers: 3 6
Before swapping: a = 3, b=6
After swapping: a = 6, b=6

Question:Simple program of c find the largest number 

#include<stdio.h>
int main(){
  int n,num,i;
  int big;
  
  printf("Enter the values of n: ");
  scanf("%d",&n);
 
  printf("Number %d",1);
  scanf("%d",&big);

  for(i=2;i<=n;i++){
    printf("Number %d: ",i);
    scanf("%d",&num);

    if(big<num)
      big=num;
  }
  
  printf("Largest number is: %d",big);

  return 0;
}
Sample Output:
Enter the values of n:
Number 1: 12
Number 2: 32
Number 3: 35
Largest number is: 35

Question:Extract digits from integer in c language 

#include<stdio.h>
int main(){
  int num,temp,factor=1;

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

  temp=num;
  while(temp){
      temp=temp/10;
      factor = factor*10;
  }

  printf("Each digits of given number are: ");
  while(factor>1){
      factor = factor/10;
      printf("%d ",num/factor);
      num = num % factor;
  }

  return 0;
}
Sample output:
Enter a number: 123
Each digits of given number are: 1 2 3

Question:Count the number of digits in c programming language 

#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

Question:C code to count the total number of digit using for loop 

#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

Question:Count the digits of a given number in c language using recursion 

#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