MCS-201 – Programming in C and Python is the first subject of IGNOU PGDCA (new). The difference between call by value and call by reference was asked in the June 2026 term-end paper, and it is a common short question.
The difference in brief
| Point | Call by value | Call by reference |
| What is passed | A copy of the variable's value | The address of the variable (a pointer) |
| Effect on original | The original variable does not change | Changes inside the function change the original |
| Function header in C | void swap(int a, int b) |
void swap(int *a, int *b) |
| Function call | swap(x, y); |
swap(&x, &y); |
Exam tip
- Write the same
swap()program both ways and show the output, so the examiner sees that only call by reference swaps the values. - Mention that C itself passes arguments by value, and call by reference is achieved by passing pointers.
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