[C언어 #13] 입력한 숫자까지의 합

C언어 입력한 숫자까지의 합

 

 

Sum from 1 to input number - for loop

/* Sum from 1 to input number - for loop */
#include <stdio.h>
 
int getInputNumber() {
    int input = 0;
    printf("Input an integer: ");
    scanf("%d", &input);
    return input;
}
 
int getSum(int input) {
    int sum = 0;    
    for (int i = 1; i <= input; i++ ) {
        sum += i;
    }
    return sum;
}
 
void print(int num, int sum) {
    printf("Sum from 1 to %d is '%d'", num, sum);
}
 
int main() {
    int num = getInputNumber();
    int sum = getSum(num);
    print(num, sum);
    return 0;
}

 

 

Sum from 1 to input number - recursion

/* Sum from 1 to input number - recursion */
#include <stdio.h>
 
/* Get input number */
int getInputNumber() {
    int input = 0;
    printf("Input an integer: ");
    scanf("%d", &input);
    return input;
}
 
/* Recursion */
int getSum(int input) {
    if (input == 1) return 1;
    else return input + getSum(input-1);
}
 
/* Print result */
void print(int num, int sum) {
    printf("Sum from 1 to %d is '%d'", num, sum);
}
 
int main() {
    int num = getInputNumber();
    print(num, getSum(num));
    return 0;
}

 

 

 

 

Input number test - Sum

/* Input number test - Sum */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <stdbool.h>
 
bool isValid(int n, const char input[]) {
    if (input[0] == '0') return false;
    for (int i = 0; i < n; i++) if (!isdigit(input[i])) return false;
    return true;
}
 
int convert(int n, const char input[]) {
    return isValid(n, input) ? atoi(input) : -1;
}
 
int add(int n) {
    int sum = 0;
    for (int i = 1; i <= n; i++) {
        sum += i;
    }
    return sum;
}
 
int main(int n, char *args[n]) {
    setbuf(stdout, NULL);
    if (n == 1) {
        return 0;
    } else if (n == 2) {
        int num = convert(strlen(args[1]), args[1]);
        if (num == -1) {
            printf("Invalid input!!\n");
            fprintf(stderr, "Try:   ./intest_2    or   ./intest_2 integer\n");
            fprintf(stderr, "ex. ./intest_2 22\n");
        } else {
            int sum = add(num);
            printf("Sum from 1 to %d is '%d'", num, sum);
        }
    } else {
        fprintf(stderr, "Try:   ./intest_2    or   ./intest_2 integer\n");
        fprintf(stderr, "ex. ./intest_2 22\n");
    }
    return 0;
}

 

.\intest_2 11