C program to check whether triangle is valid or not if sides are given

Example
Input

Input first side: 7
Input second side: 10
Input third side: 5

Output

Triangle is valid

Property of triangle

A triangle is valid if sum of its two sides is greater than the third side. Means if a, b, c are three sides of a triangle. Then the triangle is valid if all three conditions are satisfied
a + b > c
a + c > b and
b + c > a

Logic to check triangle validity

Step by step descriptive logic to check triangle validity if its sides are given.

1. Input sides of a triangle from user. Store them in some variable say side1, side2 and side1.
2. Given triangle is valid if side1 + side2 > side3 and side1 + side3 > side2 and side2 + side3 > side1.

Program to check triangle validity using nested if...else

/**
 * C program to check whether a triangle is valid or not if its sides are given
 */

#include <stdio.h>

int main()
{
    int side1, side2, side3;

    /* Input three sides of a triangle */
    printf("Enter three sides of triangle: \n");
    scanf("%d%d%d", &side1, &side2, &side3);
    
    if((side1 + side2) > side3)
    {
        if((side2 + side3) > side1)
        {
            if((side1 + side3) > side2) 
            {
                /*
                 * If side1 + side2 > side3 and
                 *    side2 + side3 > side1 and
                 *    side1 + side3 > side2 then
                 * the triangle is valid.
                 */
                printf("Triangle is valid.");
            }
            else
            {
                printf("Triangle is not valid.");
            }
        }
        else
        {
            printf("Triangle is not valid.");
        }
    }
    else
    {
        printf("Triangle is not valid.");
    }

    return 0;
}

/*
Output :

Enter three sides of triangle: 7
4
10
Triangle is valid.
*/

Program to check valid triangle using nested if

/** 
 * C program to check whether a triangle is valid using nested if 
 */  
  
#include <stdio.h>  
  
int main()  
{  
    int side1, side2, side3; 

    /* Initially assume that the triangle is not valid */
    int valid = 0;
  
    /* Input all three sides of a triangle */  
    printf("Enter three sides of triangle: \n");  
    scanf("%d%d%d", &side1, &side2, &side3);  
      
    if((side1 + side2) > side3)  
    {  
        if((side2 + side3) > side1)  
        {  
            if((side1 + side3) > side2)
            {  
                /*
                 * If side1 + side2 > side3 and
                 *    side2 + side3 > side1 and
                 *    side1 + side3 > side2 then
                 * the triangle is valid. Hence set
                 * valid variable to 1.
                 */
                valid = 1;
            }  
        }
    }  
    
    /* Check valid flag variable */
    if(valid == 1)
    {
        printf("Triangle is valid.");
    }
    else
    {
        printf("Triangle is not valid.");
    }
  
    return 0;  
}

/*
Output :

Enter three sides of triangle: 7
4
10
Triangle is valid.
*/

Program to check valid triangle using if...else and logical AND operator

/**
 * C program to check whether a triangle is valid or not using logical AND operator
 */

#include <stdio.h>

int main()
{
    int side1, side2, side3;

    /* Input all three sides of a triangle */
    printf("Enter three sides of triangle: \n");
    scanf("%d%d%d", &side1, &side2, &side3);

    if((side1 + side2 > side3) && (side1 + side3 > side2) && (side2 + side3 > side1))
    {
        printf("Triangle is valid.");
    }
    else
    {
        printf("Triangle is not valid.");
    }

    return 0;
}

/*
Output :

Enter three sides of triangle: 7
4
10
Triangle is valid.
*/