Conditionals

Branching lets a program take different paths depending on a condition. In C, any nonzero value counts as "true" and 0 counts as "false" — there's no separate boolean type to reason about, just numbers.

if, else if, else

1#include <stdio.h>
2 
3int main(void) {
4    int score = 82;
5 
6    if (score >= 90) {
7        printf("A\n");
8    } else if (score >= 80) {
9        printf("B\n");
10    } else if (score >= 70) {
11        printf("C\n");
12    } else {
13        printf("F\n");
14    }
15    return 0;
16}

Conditions are checked top to bottom, and the first true branch runs — the rest are skipped, even if they'd also be true.

1if (score >= 90)
2    printf("A\n");
3    printf("Great job!\n");  // runs unconditionally, despite the indentation

switch

A switch compares one value against several constant cases — clearer than a long if/else if chain when you're testing a single variable for equality:

1int day = 3;
2 
3switch (day) {
4    case 1:
5        printf("Monday\n");
6        break;
7    case 2:
8        printf("Tuesday\n");
9        break;
10    case 3:
11        printf("Wednesday\n");
12        break;
13    default:
14        printf("Some other day\n");
15}

The ternary operator

For a simple choice between two values, the ternary operator ?: is a compact alternative to a full if/else:

1int max = (a > b) ? a : b;
2// equivalent to:
3// int max; if (a > b) { max = a; } else { max = b; }