Control flow and loops

if, switch, the three loops, and the off-by-one errors that cost marks.

11 min read · Lesson 4 of 6 · Pro

Programs make decisions

Without branching, a program is a fixed list of steps. if is what makes it react to data.

#include <stdio.h>

int main(void)
{
    int marks;
    printf("Marks: ");
    if (scanf("%d", &marks) != 1) return 1;

    if (marks >= 90)
        printf("Grade O\n");
    else if (marks >= 75)
        printf("Grade A\n");
    else if (marks >= 40)
        printf("Grade B\n");
    else
        printf("Fail\n");

    return 0;
}

The order matters. Because the checks run top to bottom and stop at the first true one, marks = 95 never reaches the >= 75 test. Write the ranges from highest to lowest and the logic stays simple.

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