Written: August 22, 2026
A [5][3] marks table is the usual intro to 2D arrays in GTU labs.
This walkthrough keeps the logic small and readable so you can type it, run it, and then change one input at a time to see what happens.
What you will build
You will fill marks[5][3], sum each row, and print totals/averages.
- Declare float marks[5][3]
- Read marks with nested loops
- Sum each student row
- Print total and average
Working C example
#include <stdio.h>
int main(void) {
float marks[5][3], total, avg;
int i, j;
for (i = 0; i < 5; i++) {
printf("Marks for student %d (3 subjects): ", i + 1);
for (j = 0; j < 3; j++) scanf("%f", &marks[i][j]);
}
for (i = 0; i < 5; i++) {
total = 0;
for (j = 0; j < 3; j++) total += marks[i][j];
avg = total / 3.0f;
printf("Student %d -> Total %.2f Average %.2f\n", i + 1, total, avg);
}
return 0;
}How the logic works
Read the program top to bottom: includes and main first, then the statements that change variables, then the print that proves the result.
If your output looks wrong, print the variables before and after the critical lines. That single habit catches most beginner bugs faster than rewriting the whole file.
Keep student index as the outer loop so each row stays one person.
Common mistakes
Forgetting a semicolon, using the wrong format specifier in printf/scanf, and mixing up assignment (=) with comparison (==) are the usual culprits.
Compile with warnings enabled (`gcc -Wall`) so the compiler points at risky casts and unused variables before you chase them by hand.
Try this next
Change the sample inputs, add a second test case, and briefly note what stayed the same. Teaching yourself with tiny experiments sticks better than copying a longer program you never run.
When you can explain every line without looking, you are ready for the next exercise in the series.
Keep learning
If this walkthrough on 5 students 3 subjects average c helped, open the code again and change one input or assumption. Small experiments beat rereading the same example.
Want more step-by-step tutorials like this? Browse blog.xqa.io — and tell us which topic you want next.
