Shortcut Ways to Write if in C: the Ternary Operator and More

Shorten an if to one line by dropping the braces, write an if-else with the ternary operator ?:, and use other shortcuts: testing a value directly and using a comparison as a number. With short examples and their real output.

Reading 15 min

By the end of this lesson you will

• Write an if-else as one expression with ?:
• Use other if shortcuts safely

Resources

• Conditional operator

The ternary operator replaces a five-line if-else with one expression.

A short if takes three lines, and an if-else that only chooses a value takes five. C has a few shortcuts for these small decisions. Every program below was compiled with gcc -Wall -Wextra and run; the outputs are real. For the long form, see if-else examples in C.

1. Start Simple: Drop the Braces

Here is a very common piece of code, inside a loop that should skip the number 4. The long form:

if (i == 4) {
    continue;
}

The braces { } are needed only to group several statements. When the body is a single statement, we can leave them out, and the whole if fits on one line:

if (i == 4) continue;

Same meaning, two lines shorter. In a complete program:

for (int i = 1; i <= 6; i++) {
    if (i == 4) continue;
    printf("%d ", i);
}
printf("\n");

1 2 3 5 6 

The number 4 is skipped. (Section 5 shows the one trap of this shortcut.)

2. The Ternary Operator ? :

An if-else that only chooses a value can shrink too. The pattern is condition ? value_if_true : value_if_false. It is an expression: it produces a value we can assign, return or print. First, the long form:

int a = 7, b = 12;
int max;
if (a > b) {
    max = a;
} else {
    max = b;
}

The shortcut:

int max = a > b ? a : b;

Both give 12. Read the shortcut aloud as “is a greater than b? then a, otherwise b”. Together in a runnable program:

#include <stdio.h>

int main(void) {
    int a = 7, b = 12;
    int max = a > b ? a : b;
    printf("%d\n", max);
    return 0;
}

12

Example: choose a word inside printf

Because it is an expression, it fits inside a function call, which is where it is most useful:

for (int n = 3; n <= 4; n++) {
    printf("%d is %s\n", n, n % 2 == 0 ? "even" : "odd");
}
int items = 1;
printf("%d item%s\n", items, items == 1 ? "" : "s");
items = 3;
printf("%d item%s\n", items, items == 1 ? "" : "s");

3 is odd
4 is even
1 item
3 items

The second pattern, adding an s only when the count is not 1, is a classic.

Example: absolute value and clamping

int n = -5, low = 0, high = 10, x = 15;
int abs_n = n < 0 ? -n : n;
int clamped = x < low ? low : (x > high ? high : x);
printf("abs = %d, clamped = %d\n", abs_n, clamped);

abs = 5, clamped = 10

The second line nests a ternary inside another: below low gives low, above high gives high, otherwise x. One level of nesting is fine; beyond that, write a normal if.

Warning

Keep it readable. A chain such as score >= 80 ? 'A' : score >= 60 ? 'B' : 'C' works (it printed A for 85), but three or more levels are harder to read than the if/else if they replace. The ternary is a shortcut for a simple choice between two values. It is not a replacement for if when the branches do things (several statements, loops, return).

3. Test a Value Directly

In C, zero is false and any other value is true. So we don’t need to compare with 0:

int count = 3, done = 0;
if (count)  printf("count is non-zero\n");   // same as count != 0
if (!done)  printf("not done yet\n");        // same as done == 0

count is non-zero
not done yet

if (x) means “x is not zero”; if (!x) means “x is zero”. Use it for flags and counts; for a number where zero is a meaningful value (a score, a temperature), the explicit != 0 is clearer.

4. A Comparison Is a Number

A comparison gives 1 when true and 0 when false, so it can be stored or added:

int year = 2100;
int leap = (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
printf("%d leap? %d\n", year, leap);

int a = 5, b = 3;
printf("a > b gives %d, a < b gives %d\n", a > b, a < b);

// counting with a condition: no if needed
int nums[] = {4, 9, 2, 7, 10, 3}, big = 0;
for (int i = 0; i < 6; i++) {
    big += nums[i] > 5;
}
printf("numbers above 5: %d\n", big);

2100 leap? 0
a > b gives 1, a < b gives 0
numbers above 5: 3

big += nums[i] > 5; adds 1 for every element above 5 and 0 otherwise, replacing if (nums[i] > 5) big++;. (2100 is not a leap year: divisible by 100 but not by 400.)

5. The Trap of Braces-Free if

The shortcut in section 1 works because the body is a single statement. The trap is adding a second one later. Only the first statement after the if belongs to it, whatever the indentation says:

int n = -1;
if (n > 0)
    printf("one\n");
    printf("two (always printed!)\n");

two (always printed!)

n is not positive, yet the second printf runs, because it is not part of the if. With -Wall, gcc even warns: this 'if' clause does not guard... [-Wmisleading-indentation]. The fix is to keep the braces whenever the body might grow:

if (n > 0) {
    printf("one\n");
    printf("two\n");
}

6. Lookup Instead of if/else if

When a number picks one of several fixed texts, an array beats a chain of ifs:

int month = 3;
const char *name[] = {"Jan", "Feb", "Mar", "Apr"};
printf("%s\n", name[month - 1]);

Mar

Precedence and Type Pitfalls

int x = 4;
int r = x % 2 == 0 ? 10 : 20;
int p = 1 + x > 3 ? 100 : 200;   // 1 + x is computed, then > 3, then ?:
printf("%d %d\n", r, p);
printf("%.1f\n", 5 > 3 ? 1.5 : 2);

10 100
1.5

• ?: has low precedence: the whole condition is evaluated first. When in doubt, add parentheses around the condition, and around a ternary used inside a bigger expression.
• If the two values have different types (1.5 and 2), the result takes the common type (double). Use the matching format (%.1f, not %d).

Summary

Shortcut	Replaces	Use when
x = c ? a : b;	if (c) x = a; else x = b;	choosing one of two values
printf("%s", c ? "yes" : "no");	an if around two printfs	picking text inside output
if (x) / if (!x)	x != 0 / x == 0	flags and counts
count += cond;	if (cond) count++;	counting matches
if (c) stmt;	if (c) { stmt; }	one short statement, no later additions
name[i]	a chain of else if	an index selects a fixed value

• cond ? a : b is an expression that picks a value.
• Use it for choosing a value, not for long branches.
• Parenthesise it inside bigger expressions.

Expression. Code that produces a value, unlike a statement such as if.