RCU 21BCA1C1P · Lab Program 2

Largest of Three Numbers in C

Read three integers and print the largest one, using an if-else ladder.

Algorithm

Read three integers a, b and c.
If a is at least as large as b and c, a is the largest.
Otherwise, if b is at least as large as c, b is the largest.
Otherwise c is the largest.

C program

#include <stdio.h>

int main(void) {
    int a, b, c, largest;

    printf("Enter three integers:\n");
    if (scanf("%d %d %d", &a, &b, &c) != 3) {
        printf("Error: invalid input\n");
        return 1;
    }

    if (a >= b && a >= c) {
        largest = a;
    } else if (b >= c) {
        largest = b;
    } else {
        largest = c;
    }

    printf("Largest: %d\n", largest);
    return 0;
}

Sample input and output

Middle value is largest

Input

3 9 4

Output

Enter three integers:
Largest: 9

Edge case: all three equal

Input

5 5 5

Output

Enter three integers:
Largest: 5

How the program works

The first test uses >= so that ties are handled without a special case. Once a is ruled out as the largest, only b and c remain, and the second test decides between them.

Using a ladder of conditions means each value is compared only as many times as needed.

Run this code

Edit the program and press Run. It is free and needs no sign-in.

Program input (what the program reads with scanf)

Copy a sample and paste it into the STDIN box in the editor before you press Run.

Middle value is largest
```
3 9 4
```
Expected output
```
Enter three integers:
Largest: 9
```
Edge case: all three equal
```
5 5 5
```
Expected output
```
Enter three integers:
Largest: 5
```

Viva questions

Why does the first condition use >= rather than >?

So that when two or more values are equal to the maximum, the program still returns that value.

How many comparisons does the program make in the worst case?

Three comparisons, since the last branch needs no test.

Could the same result be written with the conditional operator?

Yes, for example largest = a > b ? a : b, nested for three values.

What does scanf return and why is it checked?

The number of values read. Checking for 3 catches missing input.

Why are the comparisons nested as if-else rather than separate ifs?

An else-if ladder stops at the first true condition, so only one value is assigned.

Common mistakes

Comparing only a with b and forgetting c.
Using > where >= is needed, which returns the wrong value for ties.

Back to all RCU 21BCA1C1P lab programs.

C program

#include <stdio.h> int main(void) { int a, b, c, largest; printf("Enter three integers:\n"); if (scanf("%d %d %d", &a, &b, &c) != 3) { printf("Error: invalid input\n"); return 1; } if (a >= b && a >= c) { largest = a; } else if (b >= c) { largest = b; } else { largest = c; } printf("Largest: %d\n", largest); return 0; }

Viva questions

Why does the first condition use >= rather than >?

So that when two or more values are equal to the maximum, the program still returns that value.

How many comparisons does the program make in the worst case?

Three comparisons, since the last branch needs no test.

Could the same result be written with the conditional operator?

Yes, for example largest = a > b ? a : b, nested for three values.

What does scanf return and why is it checked?

The number of values read. Checking for 3 catches missing input.

Why are the comparisons nested as if-else rather than separate ifs?

An else-if ladder stops at the first true condition, so only one value is assigned.