How to Build a Real-Time Console Progress Bar in C

In routine server operations we often see progress bars; this guide shows how to create such a progress bar using C.

1. Carriage Return and Newline

\n moves to the next line, while \r returns to the start of the current line; in C, \n typically performs both actions.

2. Output Buffering

Two example programs illustrate buffering effects. The first prints a message, sleeps for three seconds, and the output appears immediately because the string ends with \n (line buffering). The second omits \n, so the message stays in the buffer until the program ends.

The three buffering modes are:

Unbuffered – data is written directly to the device.

Line buffered – data is flushed when a newline is encountered.

Fully buffered – data is flushed only when the buffer is full.

These examples demonstrate that the console uses line buffering.

3. Countdown Program

Printing a decreasing number with printf("%d\r", count--); and sleep(1); creates a countdown, but without a newline the output remains buffered. Adding fflush(stdout); forces the buffer to flush, making the countdown visible.

For multi‑digit counts, use a width specifier such as printf("%2d\r", count--); to keep the cursor position consistent.

4. Progress Bar Program

The following code builds a 0‑100% progress bar that updates in place:

#include <stdio.h>
#include <string.h>
#include <unistd.h>

void ProcBar() {
  int i = 0;
  char proc[102];
  memset(proc, '\0', sizeof(proc));
  while (i <= 100) {
    // left‑align within 100 characters
    printf("[%-100s] [%d%%]\r", proc, i);
    fflush(stdout);
    proc[i] = '#';
    usleep(100000); // 0.1 second
    i++;
  }
  printf("
");
}

int main() {
  ProcBar();
  return 0;
}

The program repeatedly prints a bar of # characters, updates the percentage, and flushes the output to create a smooth visual progress indicator.

Images below illustrate the behavior of the examples: