Increasing Number Triangle Using i + j - 1 in C

What You’ll Learn

The increasing number triangle using i + j - 1 prints 1, 2 3, 3 4 5, … — a natural follow-up after Program 32’s triangle starting from 11. This tutorial covers the i + j - 1 formula, nested loops, a live preview, worked C examples, edge cases, and complexity.

📝 Problem & Approach

Given rows = 5, print a left-shifted increasing triangle: for each row i, print j = 1..i values of i + j - 1 separated by spaces.

// rows = 5 (conceptual shape)
// 1
// 2 3
// 3 4 5
// 4 5 6 7
// 5 6 7 8 9

Inputs & Outputs

Minimal workflow

for i from 1 to rows:
    for j from 1 to i:
        print (i + j - 1) + space
    print newline

Approach comparison

🔮 Live Preview

Choose a row count between 3 and 9 and draw the increasing triangle in the browser.

Press "Draw pattern".

Examples Gallery

Three complete C programs — fixed rows, user input, and a smaller trace demo. Click View Output to reveal sample console results.

#include <stdio.h>

int main() {
    int i, j;

    for (i = 1; i <= 5; ++i) {
        for (j = 1; j <= i; ++j)
            printf("%d ", i + j - 1);

        printf("\n");
    }

    return 0;
}

1
2 3
3 4 5
4 5 6 7
5 6 7 8 9

#include <stdio.h>

int main() {
    int rows;
    int i, j;

    printf("Enter rows: ");
    scanf("%d", &rows);
    if (rows < 1) return 0;

    for (i = 1; i <= rows; ++i) {
        for (j = 1; j <= i; ++j)
            printf("%d ", i + j - 1);

        printf("\n");
    }

    return 0;
}

Enter rows: 3
1
2 3
3 4 5

#include <stdio.h>

int main() {
    int rows = 3;
    int i, j;

    for (i = 1; i <= rows; ++i) {
        for (j = 1; j <= i; ++j)
            printf("%d ", i + j - 1);

        printf("\n");
    }

    return 0;
}

1
2 3
3 4 5

🔎 Worked Walkthrough — rows = 5

Trace each outer-loop value of i, inner-loop range, values printed, and full row output.

Prints per row = i — total prints = n(n+1)/2 for n rows.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices