6. Pointer[C Basic]

6.1.

Write program using pointer

The function should receive three integer pointer:

1. Increase 1st argument by 1

2. Multiply 2nd argument by 3rd argument

3. Assign the result to 2nd argument

4. Swap 2nd and 3rd argument

#include<stdio.h>

cal(int *a, int *b, int *c) {
	(*a)++;
	(*b) *= (*c);
	int temp = *b;
	*b = *c;
	*c = temp;
}

int main()
{
	int a, b, c;
	printf("Enter three numbers: ");
	scanf("%d %d %d", &a, &b, &c);
	printf("Before: a = %d, b = %d, c = %d\n", a, b, c);
	cal(&a, &b, &c);
	printf("After: a = %d, b = %d, c = %d\n", a, b, c);
	
	return 0;
}

 

6.2.

Write a function that receives two strings and compares the input strings. 

If two strings are same, return 1; otherwise, return 0. 

char string1[80]; char string2 [80]; 

Using a call-by-reference

#include<stdio.h>
int check_string(char str1[80], char str2[80]) {
	//const는 값을 바꿀 수 없는 상태가 된다 > 읽기만 가능
	while(*str1!='\0'||*str2!='\0'){
		if(*str1++!=*str2++)
			return 0;
	}
	return 1;
}
int main()
{
	char str1[80], str2[80];
	printf("Enter two strings : ");
	scanf("%s %s",str1, str2);

	if (check_string(str1, str2))
		printf("%s and %s are equal.", str1, str2);
	else
		printf("%s and %s are not equal.", str1, str2);
	//삼항연산자 strcmp

	return 0;
}

 

6.3.

Write a program that inputs two strings, and concatenates the two strings into the first one 

(e.g., s1: Hello, s2:World -> s1: HelloWorld, s2: World) 

char string1[80]; char string2 [80]; 

Using a call-by-reference

#include<stdio.h>
void concatenation(char *str1, char *str2) {
	while (*str1++ != '\0');
	*str1--;
	while (*str1++=*str2++);
}

int main()
{
	char str1[80], str2[80];
	printf("Enter two strings : ");
	scanf("%s %s",&str1,&str2);
	concatenation(str1,str2);
	printf("%s",str1);
	return 0;
}

 

6.4.

Write a program that takes operation mode and two input numbers. The program outputs the result with a full equation. 

Using a function pointer

#include<stdio.h>
int add(int *a, int *b);
int sub(int *a, int *b);
int mul(int *a, int *b);

int main()
{
	int (*func[3])(int, int) = { add, sub, mul };
	char operator[3]={'+','-','*'};
	int select, num1, num2;
		//size_y select;
	printf("0.Addition\n1.Subtraction\n2.Multiplication\n3.End\n");
	printf("select the operation : ");
	scanf("%d",&select);
	if(select!=3){
		printf("Enter the two numbers : ");
		scanf("%d %d",&num1,&num2);
		printf("\n%d %c %d = %d\n",num1,operator[select],num2,func[select](&num1,&num2));	
	}
	
	return 0;
}

int add(int *a, int *b){
	return *a+*b;
}
int sub(int *a, int *b){
	return *a-*b;
}
int mul(int *a, int *b){
	return *a**b;
}

 

6.5.

Write a program that print out an array with inverse order 

Using rand() function to initialize an array 

When you print it out, use pointer operator to access elements of the array

#include<stdio.h>
#include<time.h>
int main()
{
	srand(time(NULL));
	
	int arr[10];
	int *inverse=arr;
	int i;
	for(i=0;i<10;i++)
		arr[i]=rand()%99+1;
	
	for(i=0;i<10;i++)
		printf("%2d ",*inverse++);
	printf("\n");
	for(i=0;i<10;i++)
		printf("%2d ",*--inverse);
		
	return 0;
}