#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

#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

#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;
}

#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

#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