Difference between %d and %i format specifier in C

In C programming, both %d and %i are format specifiers used for integer values, but they behave differently when used with scanf() for input operations. For printf(), they work identically.

Syntax

printf("%d", integer_variable);   // Decimal output
printf("%i", integer_variable);   // Integer output (same as %d for printf)
scanf("%d", &integer_variable);   // Reads decimal integers only
scanf("%i", &integer_variable);   // Reads decimal, octal, and hexadecimal

Format Specifier %d

The %d format specifier handles signed decimal integers. For printf(), it displays integers in decimal form. For scanf(), it only accepts decimal input −

Example

#include <stdio.h>

int main() {
    int v1 = 7456;
    int v2 = -17346;
    printf("The value in decimal form: %d<br>", v1);
    printf("The value in negative: %d<br>", v2);
    return 0;
}

The value in decimal form: 7456
The value in negative: -17346

Format Specifier %i

The %i format specifier works identically to %d for printf(), but for scanf(), it can read decimal, octal (prefixed with 0), and hexadecimal (prefixed with 0x) values −

Example

#include <stdio.h>

int main() {
    int decimal = 1327;
    int hex = 0x1A3;     // Hexadecimal 0x1A3 = 419 decimal
    int octal = 0755;    // Octal 0755 = 493 decimal
    
    printf("Decimal value: %i<br>", decimal);
    printf("Hex value 0x1A3 as decimal: %i<br>", hex);
    printf("Octal value 0755 as decimal: %i<br>", octal);
    return 0;
}

Decimal value: 1327
Hex value 0x1A3 as decimal: 419
Octal value 0755 as decimal: 493

Key Differences

Conclusion

While %d and %i are identical for printf(), they differ significantly for scanf(). Use %d when you need decimal-only input, and %i when accepting multiple number formats.